Explicitly specify the ui::Compositor to DelegatedFrameHost

ui/aura/window_tree_host.cc

Index: ui/aura/window_tree_host.cc
diff --git a/ui/aura/window_tree_host.cc b/ui/aura/window_tree_host.cc
index 39ed6422e50ee4d266ba5ca3c8812a1e6f4539c4..b048ceb2077f5ab246f187190f634ac496baecc7 100644
--- a/ui/aura/window_tree_host.cc
+++ b/ui/aura/window_tree_host.cc
@@ -181,6 +181,8 @@ WindowTreeHost::WindowTreeHost()
 }
 
 void WindowTreeHost::DestroyCompositor() {
+  FOR_EACH_OBSERVER(WindowTreeHostObserver, observers_,

[sky, 2015/01/23 17:32:18]

Can whoever cares about this notification listen directly to the compositor?

[ccameron, 2015/01/23 18:52:27]

Sure (just checked that observers can be removed while traversing).

I still do like this version, but either seems fine to me.

+                    OnHostCompositorWillBeDestroyed(this));
   compositor_.reset();
 }