Revert 176061

> LTHI's bg animation timer should set the fake thread to impl.
> 
> The single thread proxy expects this to be true.
> 
> BUG=165399
> 
> 
> Review URL: https://chromiumcodereview.appspot.com/11532009
This is causing failures on mac:

http://build.chromium.org/p/chromium.mac/buildstatus?builder=Mac%2010.6%20Tests%20%28dbg%29%281%29&number=32119
http://build.chromium.org/p/chromium.mac/buildstatus?builder=Mac%2010.7%20Tests%20%28dbg%29%281%29&number=5885

TBR=vollick@chromium.org
Review URL: https://codereview.chromium.org/11820049

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@176075 0039d316-1c4b-4281-b951-d872f2087c98

cc/layer_tree_host_impl.cc

@@ -71,7 +71,6 @@ public:
 
     virtual void onTimerTick() OVERRIDE
     {
-        DebugScopedSetImplThread setImplThread(m_layerTreeHostImpl->proxy());
         m_layerTreeHostImpl->animate(base::TimeTicks::Now(), base::Time::Now());
     }