Change Canvas2DLayerBridge to stay alive until last mailbox is returned.

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 12f87fa0f0dd9af0e2c5a6eb8c314d46ec4bd97f..d40988c36f0a177245219310fccdf30d46b6fde6 100644
--- a/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.h
+++ b/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.h
@@ -43,6 +43,29 @@ class WebGraphicsContext3D;
 
 namespace WebCore {
 
+class Canvas2DLayerBridge;
+
+// Pointer class, for Canva2DLayerBridge. Similar to OwnPtr, with special

[Stephen White, 2013/08/20 17:32:18]

Nit: Canva -> Canvas.

+// asynchronous destruction mechanism
+class Canvas2DLayerBridgePtr {
+public:
+    Canvas2DLayerBridgePtr() { }
+    explicit Canvas2DLayerBridgePtr(Canvas2DLayerBridge* ptr) { m_ownPtr = adoptPtr(ptr); }
+    Canvas2DLayerBridgePtr(Canvas2DLayerBridgePtr& other) : m_ownPtr(other.m_ownPtr.release()) { }
+    Canvas2DLayerBridgePtr& operator=(Canvas2DLayerBridgePtr& other)
+    {
+        clear();
+        m_ownPtr = other.m_ownPtr.release();
+        return *this;
+    }
+    ~Canvas2DLayerBridgePtr() { clear(); }
+    void clear();
+    Canvas2DLayerBridge* get() const { return m_ownPtr.get(); }
+    Canvas2DLayerBridge* operator->() const { ASSERT(m_ownPtr); return m_ownPtr.get(); }
+private:
+    OwnPtr<Canvas2DLayerBridge> m_ownPtr;
+};
+
 class Canvas2DLayerBridge : public WebKit::WebExternalTextureLayerClient, public SkDeferredCanvas::NotificationClient, public DoublyLinkedListNode<Canvas2DLayerBridge> {
     WTF_MAKE_NONCOPYABLE(Canvas2DLayerBridge);
 public:
@@ -51,9 +74,9 @@ public:
         NonOpaque
     };
 
-    static PassOwnPtr<Canvas2DLayerBridge> create(PassRefPtr<GraphicsContext3D>, const IntSize&, OpacityMode);
+    static Canvas2DLayerBridgePtr create(PassRefPtr<GraphicsContext3D>, const IntSize&, OpacityMode);
 
-    virtual ~Canvas2DLayerBridge();
+    virtual ~Canvas2DLayerBridge(); // should not be called directly
 
     // WebKit::WebExternalTextureLayerClient implementation.
     virtual WebKit::WebGraphicsContext3D* context() OVERRIDE;
@@ -84,6 +107,9 @@ public:
 protected:
     Canvas2DLayerBridge(PassRefPtr<GraphicsContext3D>, SkDeferredCanvas*, OpacityMode);
     void setRateLimitingEnabled(bool);
+    void destroy();
+    void deleteIfPossible();
+    friend class Canvas2DLayerBridgePtr;
 
     SkDeferredCanvas* m_canvas;
     OwnPtr<WebKit::WebExternalTextureLayer> m_layer;
@@ -93,6 +119,7 @@ protected:
     bool m_surfaceIsValid;
     int m_framesPending;
     bool m_rateLimitingEnabled;
+    bool m_destructionInProgress;
 
     friend class WTF::DoublyLinkedListNode<Canvas2DLayerBridge>;
     Canvas2DLayerBridge* m_next;
@@ -118,6 +145,12 @@ protected:
     Vector<MailboxInfo> m_mailboxes;
 };
 
+inline void Canvas2DLayerBridgePtr::clear()
+{
+    if (m_ownPtr)
+        m_ownPtr.leakPtr()->destroy();

[Stephen White, 2013/08/20 17:32:18]

This looks kind of error-prone to me.

+}
+
 }
 
 #endif