Adding blink side flag that allows disabling YUV decoding

Source/platform/graphics/DecodingImageGenerator.h

Index: Source/platform/graphics/DecodingImageGenerator.h
diff --git a/Source/platform/graphics/DecodingImageGenerator.h b/Source/platform/graphics/DecodingImageGenerator.h
index a7e228d9183a623aa7bc9175b814bdc164f029b7..36acaca2a923a651684ee1b98f79cddf22b7aca8 100644
--- a/Source/platform/graphics/DecodingImageGenerator.h
+++ b/Source/platform/graphics/DecodingImageGenerator.h
@@ -49,6 +49,9 @@ public:
 
     void setGenerationId(size_t id) { m_generationId = id; }
 
+    static void setDecodeToYUVEnabled(bool);
+    static bool decodeToYUVEnabled();
+
 protected:
     virtual SkData* onRefEncodedData() OVERRIDE;
     virtual bool onGetInfo(SkImageInfo*) OVERRIDE;
@@ -60,6 +63,8 @@ private:
     SkImageInfo m_imageInfo;
     size_t m_frameIndex;
     size_t m_generationId;
+
+    static bool s_decodeToYUVEnabled;
 };
 
 } // namespace blink