Fixes leak/crash in CompositorCC.

ui/gfx/compositor/compositor_cc.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/compositor/compositor_cc.h"
 
 #include "base/command_line.h"
 #include "third_party/skia/include/images/SkImageEncoder.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebCompositor.h"
@@ skipping 127 matching lines @@
       command_line->HasSwitch(switches::kUIShowLayerTree);
 #ifndef WEBCOMPOSITOR_HAS_INITIALIZE
   settings.enableCompositorThread = !!g_compositor_thread;
 #endif
   host_ = WebKit::WebLayerTreeView::create(this, root_web_layer_, settings);
   root_web_layer_.setAnchorPoint(WebKit::WebFloatPoint(0.f, 0.f));
   OnWidgetSizeChanged();
 }
 
 CompositorCC::~CompositorCC() {
+  // There's a cycle between |root_web_layer_| and |host_|, which results in
+  // leaking and/or crashing. Explicitly set the root layer to NULL so the cycle
+  // is broken.
+  host_.setRootLayer(NULL);
 }
 
 void CompositorCC::Initialize(bool use_thread) {
   if (use_thread)
     g_compositor_thread = new webkit_glue::WebThreadImpl("Browser Compositor");
 #ifdef WEBCOMPOSITOR_HAS_INITIALIZE
   WebKit::WebCompositor::initialize(g_compositor_thread);
 #else
   if (use_thread)
     WebKit::WebCompositor::setThread(g_compositor_thread);
@@ skipping 117 matching lines @@
   ScheduleDraw();
 }
 
 Compositor* Compositor::Create(CompositorDelegate* owner,
                                gfx::AcceleratedWidget widget,
                                const gfx::Size& size) {
   return new CompositorCC(owner, widget, size);
 }
 
 }  // namespace ui