Swap best bitwriter and histo reference instead of cloning

src/ImageSharp/Formats/WebP/Lossless/PredictorEncoder.cs

@@ -294,12 +294,9 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
 
                 if (curDiff < bestDiff)
                 {
-                    // TODO: Consider swapping references
-                    for (int i = 0; i < 4; i++)
-                    {
-                        histoArgb[i].AsSpan().CopyTo(bestHisto[i]);
-                    }
-
+                    int[][] tmp = histoArgb;
+                    histoArgb = bestHisto;
+                    bestHisto = tmp;
                     bestDiff = curDiff;
                     bestMode = mode;
                 }

src/ImageSharp/Formats/WebP/Lossless/Vp8LEncoder.cs

@@ -613,8 +613,9 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                 // Keep track of the smallest image so far.
                 if (isFirstIteration || (bitWriterBest != null && this.bitWriter.NumBytes() < bitWriterBest.NumBytes()))
                 {
-                    // TODO: This was done in the reference by swapping references, this will be slower.
-                    bitWriterBest = this.bitWriter.Clone();
+                    Vp8LBitWriter tmp = this.bitWriter;
+                    this.bitWriter = bitWriterBest;
+                    bitWriterBest = tmp;
                 }
 
                 isFirstIteration = false;

src/ImageSharp/Formats/WebP/Lossy/Vp8EncIterator.cs

@@ -885,7 +885,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             this.SetCountDown(this.mbw * this.mbh);
             this.InitTop();
 
-            // TODO: memset(it->bit_count_, 0, sizeof(it->bit_count_));
+            Array.Clear(this.BitCount, 0, this.BitCount.Length);
         }
 
         /// <summary>

tests/ImageSharp.Tests/Formats/WebP/WebpEncoderTests.cs

@@ -83,9 +83,9 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
         [Theory]
         [WithFile(RgbTestPattern100x100, PixelTypes.Rgba32, 85)]
         [WithFile(RgbTestPattern100x100, PixelTypes.Rgba32, 60)]
-        [WithFile(RgbTestPattern100x100, PixelTypes.Rgba32, 40)]
-        [WithFile(RgbTestPattern100x100, PixelTypes.Rgba32, 20)]
-        [WithFile(RgbTestPattern100x100, PixelTypes.Rgba32, 10)]
+        [WithFile(RgbTestPattern80x80, PixelTypes.Rgba32, 40)]
+        [WithFile(RgbTestPattern80x80, PixelTypes.Rgba32, 20)]
+        [WithFile(RgbTestPattern80x80, PixelTypes.Rgba32, 10)]
         [WithFile(RgbTestPattern63x63, PixelTypes.Rgba32, 40)]
         public void Encode_Lossless_WithNearLosslessFlag_Works<TPixel>(TestImageProvider<TPixel> provider, int nearLosslessQuality)
             where TPixel : unmanaged, IPixel<TPixel>

tests/ImageSharp.Tests/TestImages.cs

@@ -509,6 +509,7 @@ namespace SixLabors.ImageSharp.Tests
             public const string TestPatternOpaque = "WebP/testpattern_opaque.png";
             public const string TestPatternOpaqueSmall = "WebP/testpattern_opaque_small.png";
             public const string RgbTestPattern100x100 = "WebP/rgb_pattern_100x100.png";
+            public const string RgbTestPattern80x80 = "WebP/rgb_pattern_80x80.png";
             public const string RgbTestPattern63x63 = "WebP/rgb_pattern_63x63.png";
 
             // Test image for encoding image with a palette.

tests/Images/Input/WebP/rgb_pattern_80x80.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:f4e27705d23ff33dbac5bdfe8e7e75a6eeda359ff343594fb07feb29abbc2fb5
+size 19393