[wip] Add canvas.toDataURL("image/png") compression control

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

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 21 matching lines @@
 #define PNGImageEncoder_h
 
 #include "wtf/Vector.h"
 
 class SkBitmap;
 
 namespace WebCore {
 
 struct ImageDataBuffer;
 
-// Interface for encoding PNG data. This is a wrapper around libpng.
 class PNGImageEncoder {
 public:
-    static bool encode(const SkBitmap&, Vector<unsigned char>* output);
-    static bool encode(const ImageDataBuffer&, Vector<unsigned char>* output);
+    // Encode the input data with a compression quality in [0-100].
+    static bool encode(const SkBitmap&, int quality, Vector<unsigned char>* output);
+    static bool encode(const ImageDataBuffer&, int quality, Vector<unsigned char>* output);
+
+    // For callers: provide a reasonable compression quality default.
+    enum Quality { DefaultCompressionQuality = 30 };
 };
 
 } // namespace WebCore
 
 #endif