WebGL: Don't destroy mailbox textures in the destructor until they're released.

Source/platform/graphics/gpu/DrawingBuffer.h

Index: Source/platform/graphics/gpu/DrawingBuffer.h
diff --git a/Source/platform/graphics/gpu/DrawingBuffer.h b/Source/platform/graphics/gpu/DrawingBuffer.h
index 9e69e0984cebf6ba4543b20a6be767e7f56e3b68..ef96ecc814e81756856e3b2b532a8890cdae94df 100644
--- a/Source/platform/graphics/gpu/DrawingBuffer.h
+++ b/Source/platform/graphics/gpu/DrawingBuffer.h
@@ -79,10 +79,14 @@ public:
         Discard
     };
 
-    static PassRefPtr<DrawingBuffer> create(blink::WebGraphicsContext3D*, const IntSize&, PreserveDrawingBuffer, PassRefPtr<ContextEvictionManager>);
+    static PassRefPtr<DrawingBuffer> create(PassOwnPtr<blink::WebGraphicsContext3D>, const IntSize&, PreserveDrawingBuffer, PassRefPtr<ContextEvictionManager>);
 
     virtual ~DrawingBuffer();
 
+    // Clear all resources from this object, as well as context. Called when context is destroyed
+    // to prevent invalid accesses to the resources.
+    void releaseResources();
+
     // Issues a glClear() on all framebuffers associated with this DrawingBuffer. The caller is responsible for
     // making the context current and setting the clear values and masks. Modifies the framebuffer binding.
     void clearFramebuffers(GLbitfield clearMask);
@@ -138,13 +142,11 @@ public:
     PassRefPtr<Uint8ClampedArray> paintRenderingResultsToImageData(int&, int&);
 
 private:
-    DrawingBuffer(blink::WebGraphicsContext3D*, bool multisampleExtensionSupported,
+    DrawingBuffer(PassOwnPtr<blink::WebGraphicsContext3D>, bool multisampleExtensionSupported,
                   bool packedDepthStencilExtensionSupported, PreserveDrawingBuffer, PassRefPtr<ContextEvictionManager>);
 
     bool initialize(const IntSize&);
-    // Clear all resources from this object, as well as context. Called when context is destroyed
-    // to prevent invalid accesses to the resources.
-    void releaseResources();
+    void releaseSelf(const blink::WebExternalTextureMailbox&);
 
     unsigned createColorTexture(const IntSize& size = IntSize());
     // Create the depth/stencil and multisample buffers, if needed.
@@ -196,7 +198,7 @@ private:
     Platform3DObject m_framebufferBinding;
     GLenum m_activeTextureUnit;
 
-    blink::WebGraphicsContext3D* m_context;
+    OwnPtr<blink::WebGraphicsContext3D> m_context;
     IntSize m_size;
     bool m_multisampleExtensionSupported;
     bool m_packedDepthStencilExtensionSupported;
@@ -237,6 +239,8 @@ private:
     Vector<RefPtr<MailboxInfo> > m_textureMailboxes;
     // Mailboxes that were released by the compositor and can be used again by this DrawingBuffer.
     Vector<RefPtr<MailboxInfo> > m_recycledMailboxes;
+    // This class will be destructed after all mailboxes are received.
+    RefPtr<DrawingBuffer> m_selfToWaitForMailboxes;
 
     RefPtr<ContextEvictionManager> m_contextEvictionManager;