Register clipboard image blob in the browser process to copy data less.

third_party/WebKit/public/platform/WebMockClipboard.h

Index: third_party/WebKit/public/platform/WebMockClipboard.h
diff --git a/third_party/WebKit/public/platform/WebMockClipboard.h b/third_party/WebKit/public/platform/WebMockClipboard.h
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+// 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 WebMockClipboard_h
+#define WebMockClipboard_h
+
+#include "public/platform/WebClipboard.h"
+#include "public/platform/WebImage.h"
+
+namespace blink {
+
+// Provides convenience methods for retrieving data from the mock clipboard
+// used in layout and unit tests.
+class WebMockClipboard : public WebClipboard {
+public:
+    virtual WebImage readRawImage(Buffer) { return WebImage(); }
+};
+
+} // namespace blink
+
+#endif