Added ContentTemplate binding to control templates.

src/Avalonia.Themes.Default/Button.xaml

@@ -14,6 +14,7 @@
                           BorderBrush="{TemplateBinding BorderBrush}"
                           BorderThickness="{TemplateBinding BorderThickness}"
                           Content="{TemplateBinding Content}"
+                          ContentTemplate="{TemplateBinding ContentTemplate}"
                           Padding="{TemplateBinding Padding}"
                           TextBlock.Foreground="{TemplateBinding Foreground}"
                           HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"

src/Avalonia.Themes.Default/CheckBox.xaml

@@ -22,6 +22,7 @@
           </Border>
           <ContentPresenter Name="PART_ContentPresenter"
                             Content="{TemplateBinding Content}"
+                            ContentTemplate="{TemplateBinding ContentTemplate}"
                             Margin="4,0,0,0"
                             VerticalAlignment="Center"
                             Grid.Column="1"/>

src/Avalonia.Themes.Default/DropDown.xaml

@@ -11,6 +11,7 @@
                 BorderThickness="{TemplateBinding BorderThickness}">
           <Grid ColumnDefinitions="*,Auto">
             <ContentPresenter Content="{TemplateBinding SelectionBoxItem}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               Margin="{TemplateBinding Padding}"
                               HorizontalAlignment="Center"
                               VerticalAlignment="Center"/>

src/Avalonia.Themes.Default/DropDownItem.xaml

@@ -10,6 +10,7 @@
                           BorderBrush="{TemplateBinding BorderBrush}"
                           BorderThickness="{TemplateBinding BorderThickness}"
                           Content="{TemplateBinding Content}"
+                          ContentTemplate="{TemplateBinding ContentTemplate}"
                           HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                           VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                           Padding="{TemplateBinding Padding}"/>

src/Avalonia.Themes.Default/Expander.xaml

@@ -17,6 +17,7 @@
                               Grid.Row="1"
                               IsVisible="{TemplateBinding IsExpanded}"
                               Content="{TemplateBinding Content}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               HorizontalAlignment="Stretch"
                               VerticalAlignment="Stretch" />
           </Grid>
@@ -34,6 +35,7 @@
                               Grid.Row="0"
                               IsVisible="{TemplateBinding IsExpanded}"
                               Content="{TemplateBinding Content}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               HorizontalAlignment="Stretch"
                               VerticalAlignment="Stretch" />
           </Grid>
@@ -51,6 +53,7 @@
                               Grid.Column="1"
                               IsVisible="{TemplateBinding IsExpanded}"
                               Content="{TemplateBinding Content}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               HorizontalAlignment="Stretch"
                               VerticalAlignment="Stretch" />
           </Grid>
@@ -68,6 +71,7 @@
                               Grid.Column="0"
                               IsVisible="{TemplateBinding IsExpanded}"
                               Content="{TemplateBinding Content}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               HorizontalAlignment="Stretch"
                               VerticalAlignment="Stretch" />
           </Grid>

src/Avalonia.Themes.Default/LayoutTransformControl.xaml

@@ -6,6 +6,7 @@
                         BorderBrush="{TemplateBinding BorderBrush}"
                         BorderThickness="{TemplateBinding BorderThickness}"
                         Content="{TemplateBinding Content}" 
+                        ContentTemplate="{TemplateBinding ContentTemplate}"
                         Padding="{TemplateBinding Padding}"/>
     </ControlTemplate>
   </Setter>

src/Avalonia.Themes.Default/ListBoxItem.xaml

@@ -7,6 +7,7 @@
                           BorderBrush="{TemplateBinding BorderBrush}"
                           BorderThickness="{TemplateBinding BorderThickness}"
                           Content="{TemplateBinding Content}"
+                          ContentTemplate="{TemplateBinding ContentTemplate}"
                           Padding="{TemplateBinding Padding}"/>
       </ControlTemplate>
     </Setter>

src/Avalonia.Themes.Default/MenuItem.xaml

@@ -13,6 +13,7 @@
           <Grid ColumnDefinitions="22,13,*,20">
             <ContentPresenter Name="icon"
                               Content="{TemplateBinding Icon}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               Width="16"
                               Height="16"
                               Margin="3"
@@ -26,6 +27,7 @@
                   VerticalAlignment="Center"/>
             <ContentPresenter Name="PART_HeaderPresenter"
                               Content="{TemplateBinding Header}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               Margin="{TemplateBinding Padding}"
                               VerticalAlignment="Center"
                               Grid.Column="2">
@@ -82,6 +84,7 @@
           <Panel>
             <ContentPresenter Name="PART_HeaderPresenter"
                               Content="{TemplateBinding Header}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               Margin="{TemplateBinding Padding}">
               <ContentPresenter.DataTemplates>
                 <DataTemplate DataType="sys:String">

src/Avalonia.Themes.Default/PopupRoot.xaml

@@ -5,6 +5,7 @@
       <ContentPresenter Name="PART_ContentPresenter"
                         Background="{TemplateBinding Background}"
                         Content="{TemplateBinding Content}" 
+                        ContentTemplate="{TemplateBinding ContentTemplate}"
                         Padding="{TemplateBinding Padding}"/>
     </ControlTemplate>
   </Setter>

src/Avalonia.Themes.Default/RadioButton.xaml

@@ -21,6 +21,7 @@
                    VerticalAlignment="Center"/>
           <ContentPresenter Name="PART_ContentPresenter"
                             Content="{TemplateBinding Content}"
+                            ContentTemplate="{TemplateBinding ContentTemplate}"
                             Margin="4,0,0,0"
                             VerticalAlignment="Center"
                             Grid.Column="1"/>

src/Avalonia.Themes.Default/TabStripItem.xaml

@@ -9,6 +9,7 @@
                           BorderBrush="{TemplateBinding BorderBrush}"
                           BorderThickness="{TemplateBinding BorderThickness}"
                           Content="{TemplateBinding Content}"
+                          ContentTemplate="{TemplateBinding ContentTemplate}"
                           Padding="{TemplateBinding Padding}"/>
       </ControlTemplate>
     </Setter>

src/Avalonia.Themes.Default/ToggleButton.xaml

@@ -14,6 +14,7 @@
                           BorderBrush="{TemplateBinding BorderBrush}"
                           BorderThickness="{TemplateBinding BorderThickness}"
                           Content="{TemplateBinding Content}"
+                          ContentTemplate="{TemplateBinding ContentTemplate}"
                           Padding="{TemplateBinding Padding}"
                           TextBlock.Foreground="{TemplateBinding Foreground}"
                           HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"

src/Avalonia.Themes.Default/ToolTip.xaml

@@ -10,6 +10,7 @@
                         BorderBrush="{TemplateBinding BorderBrush}"
                         BorderThickness="{TemplateBinding BorderThickness}"
                         Content="{TemplateBinding Content}" 
+                        ContentTemplate="{TemplateBinding ContentTemplate}"
                         Padding="{TemplateBinding Padding}"/>
     </ControlTemplate>
   </Setter>

src/Avalonia.Themes.Default/Window.xaml

@@ -6,7 +6,10 @@
     <ControlTemplate>
       <Border Background="{TemplateBinding Background}">
         <AdornerDecorator>
-          <ContentPresenter Name="PART_ContentPresenter" Content="{TemplateBinding Content}" Margin="{TemplateBinding Padding}"/>
+          <ContentPresenter Name="PART_ContentPresenter" 
+                            Content="{TemplateBinding Content}" 
+                            ContentTemplate="{TemplateBinding ContentTemplate}"
+                            Margin="{TemplateBinding Padding}"/>
         </AdornerDecorator>
       </Border>
     </ControlTemplate>