Change Canvas2DLayerBridge to stay alive until last mailbox is returned.

Source/core/platform/graphics/chromium/Canvas2DLayerBridgeTest.cpp

Index: Source/core/platform/graphics/chromium/Canvas2DLayerBridgeTest.cpp
diff --git a/Source/core/platform/graphics/chromium/Canvas2DLayerBridgeTest.cpp b/Source/core/platform/graphics/chromium/Canvas2DLayerBridgeTest.cpp
index 7af3be0523371176c756197902fb1ac444e5890c..6f385db13676a7e0d3c143735c32071060da7569 100644
--- a/Source/core/platform/graphics/chromium/Canvas2DLayerBridgeTest.cpp
+++ b/Source/core/platform/graphics/chromium/Canvas2DLayerBridgeTest.cpp
@@ -57,9 +57,9 @@ public:
 
 class FakeCanvas2DLayerBridge : public Canvas2DLayerBridge {
 public:
-    static PassOwnPtr<FakeCanvas2DLayerBridge> create(PassRefPtr<GraphicsContext3D> context, SkDeferredCanvas* canvas, OpacityMode opacityMode)
+    static PassRefPtr<FakeCanvas2DLayerBridge> create(PassRefPtr<GraphicsContext3D> context, SkDeferredCanvas* canvas, OpacityMode opacityMode)
     {
-        return adoptPtr(new FakeCanvas2DLayerBridge(context, canvas, opacityMode));
+        return adoptRef(new FakeCanvas2DLayerBridge(context, canvas, opacityMode));
     }
 protected:
     FakeCanvas2DLayerBridge(PassRefPtr<GraphicsContext3D> context, SkDeferredCanvas* canvas, OpacityMode opacityMode) :
@@ -87,7 +87,7 @@ protected:
 
         ::testing::Mock::VerifyAndClearExpectations(&mainMock);
 
-        OwnPtr<Canvas2DLayerBridge> bridge = FakeCanvas2DLayerBridge::create(mainContext.release(), canvas.get(), Canvas2DLayerBridge::NonOpaque);
+        Canvas2DLayerBridgePtr bridge = FakeCanvas2DLayerBridge::create(mainContext.release(), canvas.get(), Canvas2DLayerBridge::NonOpaque);
 
         ::testing::Mock::VerifyAndClearExpectations(&mainMock);