Fixing Canvas2DLayerBridge to handle lost graphics contexts

Source/core/platform/graphics/chromium/Canvas2DLayerBridge.h

Index: Source/core/platform/graphics/chromium/Canvas2DLayerBridge.h
diff --git a/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.h b/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.h
index 510f479e5cd5dda6bfcee6c7e6c3576f1c0bafec..81221e69337a0a4996d7a932196eaa869f4c13ca 100644
--- a/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.h
+++ b/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.h
@@ -37,6 +37,8 @@
 #include <wtf/PassOwnPtr.h>
 #include <wtf/RefPtr.h>
 
+class Canvas2DLayerBridgeTest;
+
 namespace WebKit {
 class WebGraphicsContext3D;
 }
@@ -56,10 +58,7 @@ public:
         Threaded
     };
 
-    static PassOwnPtr<Canvas2DLayerBridge> create(PassRefPtr<GraphicsContext3D> context, SkDeferredCanvas* canvas, OpacityMode opacityMode, ThreadMode threading)
-    {
-        return adoptPtr(new Canvas2DLayerBridge(context, canvas, opacityMode, threading));
-    }
+    static PassOwnPtr<Canvas2DLayerBridge> create(PassRefPtr<GraphicsContext3D>, const IntSize&, OpacityMode, ThreadMode);
 
     virtual ~Canvas2DLayerBridge();
 
@@ -84,10 +83,14 @@ public:
 
     WebKit::WebLayer* layer();
     void contextAcquired();
+    SkCanvas* getCanvas() { return m_canvas; }
 
     unsigned backBufferTexture();
 
+    bool isValid();
+
 protected:
+    virtual PassRefPtr<GraphicsContext3D> getSharedContext() const; // virtual for faking
     Canvas2DLayerBridge(PassRefPtr<GraphicsContext3D>, SkDeferredCanvas*, OpacityMode, ThreadMode);
 
     SkDeferredCanvas* m_canvas;
@@ -97,6 +100,8 @@ protected:
     bool m_didRecordDrawCommand;
     int m_framesPending;
 
+    friend class ::Canvas2DLayerBridgeTest; // for unit testing
+
     friend class WTF::DoublyLinkedListNode<Canvas2DLayerBridge>;
     Canvas2DLayerBridge* m_next;
     Canvas2DLayerBridge* m_prev;