Change Canvas2DLayerBridge to stay alive until last mailbox is returned.

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

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 25 matching lines @@
 #include "wtf/DoublyLinkedList.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/RefPtr.h"
 
 namespace WebKit {
 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:
     enum OpacityMode {
         Opaque,
         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;
     virtual bool prepareMailbox(WebKit::WebExternalTextureMailbox*, WebKit::WebExternalBitmap*) OVERRIDE;
     virtual void mailboxReleased(const WebKit::WebExternalTextureMailbox&) OVERRIDE;
 
     // SkDeferredCanvas::NotificationClient implementation
     virtual void prepareForDraw() OVERRIDE;
     virtual void storageAllocatedForRecordingChanged(size_t) OVERRIDE;
     virtual void flushedDrawCommands() OVERRIDE;
@@ skipping 10 matching lines @@
     void contextAcquired();
     SkCanvas* getCanvas() { return m_canvas; }
 
     unsigned backBufferTexture();
 
     bool isValid();
 
 protected:
     Canvas2DLayerBridge(PassRefPtr<GraphicsContext3D>, SkDeferredCanvas*, OpacityMode);
     void setRateLimitingEnabled(bool);
+    void destroy();
+    void deleteIfPossible();
+    friend class Canvas2DLayerBridgePtr;
 
     SkDeferredCanvas* m_canvas;
     OwnPtr<WebKit::WebExternalTextureLayer> m_layer;
     RefPtr<GraphicsContext3D> m_context;
     size_t m_bytesAllocated;
     bool m_didRecordDrawCommand;
     bool m_surfaceIsValid;
     int m_framesPending;
     bool m_rateLimitingEnabled;
+    bool m_destructionInProgress;
 
     friend class WTF::DoublyLinkedListNode<Canvas2DLayerBridge>;
     Canvas2DLayerBridge* m_next;
     Canvas2DLayerBridge* m_prev;
 
     enum MailboxStatus {
         MailboxInUse,
         MailboxReleased,
         MailboxAvailable,
     };
 
     struct MailboxInfo {
         WebKit::WebExternalTextureMailbox m_mailbox;
         SkAutoTUnref<SkImage> m_image;
         MailboxStatus m_status;
 
         MailboxInfo(const MailboxInfo&);
         MailboxInfo() {}
     };
     MailboxInfo* createMailboxInfo();
 
     uint32_t m_lastImageId;
     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