Use dictionaries for context creation attributes. Eliminate custom bindings.

Source/core/html/canvas/ContextAttributeHelpers.h

Index: Source/core/html/canvas/ContextAttributeHelpers.h
diff --git a/Source/core/html/canvas/ContextAttributeHelpers.h b/Source/core/html/canvas/ContextAttributeHelpers.h
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+++ b/Source/core/html/canvas/ContextAttributeHelpers.h
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+// Copyright 2014 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 ContextAttributeHelpers_h
+#define ContextAttributeHelpers_h
+
+#include "core/html/canvas/Canvas2DContextAttributes.h"
+#include "core/html/canvas/CanvasContextCreationAttributes.h"
+#include "core/html/canvas/WebGLContextAttributes.h"
+#include "public/platform/WebGraphicsContext3D.h"
+
+namespace blink {
+
+class Settings;
+
+Canvas2DContextAttributes to2DContextAttributes(const CanvasContextCreationAttributes&);
+WebGLContextAttributes toWebGLContextAttributes(const CanvasContextCreationAttributes&);
+
+// Set up the attributes that can be used to initialize a WebGraphicsContext3D.
+// It's mostly based on WebGLContextAttributes, but may be adjusted based
+// on settings.
+WebGraphicsContext3D::Attributes toWebGraphicsContext3DAttributes(const WebGLContextAttributes&, const blink::WebString&, Settings*, unsigned webGLVersion);
+
+} // namespace blink
+
+#endif // ContextAttributeHelpers_h