Add UMA to HTMLCanvasElement to track image formats usage of toDataURL/toBlob

third_party/WebKit/Source/core/html/HTMLCanvasElement.h

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.h b/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
index e7bb8bbb4369218d4e700e60f7e7d6304a717fc2..9bd4bc98dc8460d4b1ff936d58938e43f7955935 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
@@ -98,7 +98,12 @@ public:
 
     bool isPaintable() const;
 
-    static String toEncodingMimeType(const String& mimeType);
+    enum RequestImageFunctionCallName {

[Justin Novosad, 2016/03/22 20:23:02]

Naming nit, you can be more concise here: EncodeReason. Consistent with other
uses of "Reason" throughout blink.

+        ToDataURL = 0,

[Justin Novosad, 2016/03/22 20:23:02]

EncodeReasonToDataURL

+        ToBlobCallback = 1,
+        NumberOfRequestedImageFunctionCallNames
+    };
+    static String toEncodingMimeType(const String& mimeType, const RequestImageFunctionCallName);
     String toDataURL(const String& mimeType, const ScriptValue& qualityArgument, ExceptionState&) const;
     String toDataURL(const String& mimeType, ExceptionState& exceptionState) const { return toDataURL(mimeType, ScriptValue(), exceptionState); }