Support lossy and lossless <canvas>.toDataURL for webp

Source/platform/image-encoders/skia/WEBPImageEncoder.h

Index: Source/platform/image-encoders/skia/WEBPImageEncoder.h
diff --git a/Source/platform/image-encoders/skia/WEBPImageEncoder.h b/Source/platform/image-encoders/skia/WEBPImageEncoder.h
index 3a0e9c2df4735161dceeeb3f66c98b0315c91583..dd7d74f36f3a7e859e0f001d412c489ac766c62f 100644
--- a/Source/platform/image-encoders/skia/WEBPImageEncoder.h
+++ b/Source/platform/image-encoders/skia/WEBPImageEncoder.h
@@ -39,8 +39,11 @@ struct ImageDataBuffer;
 
 class WEBPImageEncoder {
 public:
+    // For callers: control the compression mode: lossy or lossless.
+    enum Mode { Default = 0, Lossy = Default, Lossless };
+
     // Encode the input data with a compression quality in [0-100].
-    static bool encode(const ImageDataBuffer&, int quality, Vector<unsigned char>*);
+    static bool encode(const ImageDataBuffer&, int quality, Vector<unsigned char>*, Mode = Default);
 
     // For callers: provide a reasonable compression quality default.
     enum Quality { DefaultCompressionQuality = 80 };