Make DrawingBuffer and Canvas2DLayerBridge be cc::TextureLayerClients.

third_party/WebKit/public/platform/Platform.h

Index: third_party/WebKit/public/platform/Platform.h
diff --git a/third_party/WebKit/public/platform/Platform.h b/third_party/WebKit/public/platform/Platform.h
index 8cd3fc13aa2cd48acb67e3a643f205f667440a0e..1a173a2a6033ee74a2c5ffda941960f43f562126 100644
--- a/third_party/WebKit/public/platform/Platform.h
+++ b/third_party/WebKit/public/platform/Platform.h
@@ -54,6 +54,7 @@
 #include "WebURLError.h"
 #include "WebVector.h"
 #include "base/metrics/user_metrics_action.h"
+#include "cc/resources/shared_bitmap.h"
 
 class GrContext;
 
@@ -458,6 +459,8 @@ public:
     // the context cannot be created or initialized.
     virtual WebGraphicsContext3DProvider* createSharedOffscreenGraphicsContext3DProvider() { return nullptr; }
 
+    virtual std::unique_ptr<cc::SharedBitmap> allocateSharedBitmap(const WebSize& size) { return nullptr; }
+
     // Returns true if the platform is capable of producing an offscreen context suitable for accelerating 2d canvas.
     // This will return false if the platform cannot promise that contexts will be preserved across operations like
     // locking the screen or if the platform cannot provide a context with suitable performance characteristics.