Switching to SkDeferredCanvas factory API in preparation for constructor deprecation

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

 /*
  * 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 47 matching lines @@
     info.fAlphaType = SkImage::kPremul_AlphaType;
     return SkSurface::NewRenderTarget(gr, info);
 }
 
 PassOwnPtr<Canvas2DLayerBridge> Canvas2DLayerBridge::create(PassRefPtr<GraphicsContext3D> context, const IntSize& size, OpacityMode opacityMode)
 {
     TRACE_EVENT_INSTANT0("test_gpu", "Canvas2DLayerBridgeCreation");
     SkAutoTUnref<SkSurface> surface(createSurface(context.get(), size));
     if (!surface.get())
         return PassOwnPtr<Canvas2DLayerBridge>();
-    SkDeferredCanvas* canvas = new SkDeferredCanvas(surface);
+    SkDeferredCanvas* canvas = SkDeferredCanvas::Create(surface.get());
     OwnPtr<Canvas2DLayerBridge> layerBridge = adoptPtr(new Canvas2DLayerBridge(context, canvas, opacityMode));

[Stephen White, 2013/08/08 18:04:59]

Not new to this patch, but the ownership semantics of the deferred canvas are
really unclear here.

The canvas is allocated here, and passed to the Canavs2DLayerBridge constructor.
The bridge never refs it, but also never unrefs it, and neither does this
factory function. It seems like it's just temporarily unowned, until the
ImageBuffer refs it over in ImageBuffer, while Canvas2DLayerBridge keeps a bare
pointer to it. That seems really fragile. If you just create a bridge, and never
ref the canvas in it, it'll leak. If the bridge ever outlives the ImageBuffer,
it'll blow up (I realize that doesn't happen now, but the dependency is not
explicit).

Is there any way we could clean this up?

     return layerBridge.release();
 }
 
 Canvas2DLayerBridge::Canvas2DLayerBridge(PassRefPtr<GraphicsContext3D> context, SkDeferredCanvas* canvas, OpacityMode opacityMode)
     : m_canvas(canvas)
     , m_context(context)
     , m_bytesAllocated(0)
     , m_didRecordDrawCommand(false)
     , m_surfaceIsValid(true)
     , m_framesPending(0)
@@ skipping 263 matching lines @@
 Canvas2DLayerBridge::MailboxInfo::MailboxInfo(const MailboxInfo& other) {
     // This copy constructor should only be used for Vector reallocation
     // Assuming 'other' is to be destroyed, we swap m_image ownership
     // rather than do a refcount dance.
     memcpy(&m_mailbox, &other.m_mailbox, sizeof(m_mailbox));
     m_image.swap(const_cast<SkAutoTUnref<SkImage>*>(&other.m_image));
     m_status = other.m_status;
 }
 
 }