Implement convertToBlob() in OffscreenCanvas

third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef OffscreenCanvasModules_h
 #define OffscreenCanvasModules_h
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/offscreencanvas/OffscreenCanvas.h"
 #include "modules/ModulesExport.h"
 #include "wtf/Allocator.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class CanvasContextCreationAttributes;
 class OffscreenCanvas;
 class OffscreenCanvasRenderingContext2D;
 
 class MODULES_EXPORT OffscreenCanvasModules {
   STATIC_ONLY(OffscreenCanvasModules)
  public:
   static void getContext(ScriptState*,
                          OffscreenCanvas&,
                          const String&,
                          const CanvasContextCreationAttributes&,
                          ExceptionState&,
                          OffscreenRenderingContext&);
+
+  static ScriptPromise convertToBlob(ScriptState*,
+                                     OffscreenCanvas&,
+                                     const ImageEncodeOptions&,
+                                     ExceptionState&);
+
+ private:
+  static ImageData* toImageData(OffscreenCanvas&,
+                                SourceDrawingBuffer,
+                                SnapshotReason);
 };
 
 }  // namespace blink
 
 #endif  // OffscreenCanvasModules_h