Fixes leak/crash in CompositorCC.

ui/gfx/compositor/compositor_cc.cc

Index: ui/gfx/compositor/compositor_cc.cc
diff --git a/ui/gfx/compositor/compositor_cc.cc b/ui/gfx/compositor/compositor_cc.cc
index 3bb4542b495d10678b25c743c57a93f03a1de60f..757381ce7eba6bfb28ccd5e6b41b52e3027cf558 100644
--- a/ui/gfx/compositor/compositor_cc.cc
+++ b/ui/gfx/compositor/compositor_cc.cc
@@ -145,6 +145,10 @@ CompositorCC::CompositorCC(CompositorDelegate* delegate,
 }
 
 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) {