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 637bfbe3827bcb3e30dc14c25db096489bfbe899..06eee6bbc5e29a51017e61f0d9a2e76be2b7b82d 100644
--- a/Source/platform/image-encoders/skia/WEBPImageEncoder.h
+++ b/Source/platform/image-encoders/skia/WEBPImageEncoder.h
@@ -41,9 +41,12 @@ 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 SkBitmap&, int quality, Vector<unsigned char>*);
-    static bool encode(const ImageDataBuffer&, int quality, Vector<unsigned char>*);
+    static bool encode(const SkBitmap&, int quality, Vector<unsigned char>*, Mode = Default);
+    static bool encode(const ImageDataBuffer&, int quality, Vector<unsigned char>*, Mode = Default);
 
     // For callers: provide a reasonable compression quality default.
     enum Quality { DefaultCompressionQuality = 80 };