cc: Prohibit impl-side painting with single threaded compositing

Just a little cleanup and some extra checks.

R=danakj@chromium.org
BUG=155209


Review URL: https://chromiumcodereview.appspot.com/11827036

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175981 0039d316-1c4b-4281-b951-d872f2087c98

cc/single_thread_proxy.cc

@@ -29,6 +29,10 @@ SingleThreadProxy::SingleThreadProxy(LayerTreeHost* layerTreeHost)
 {
     TRACE_EVENT0("cc", "SingleThreadProxy::SingleThreadProxy");
     DCHECK(Proxy::isMainThread());
+    DCHECK(layerTreeHost);
+
+    // Impl-side painting not supported without threaded compositing
+    DCHECK(!layerTreeHost->settings().implSidePainting);
 }
 
 void SingleThreadProxy::start()
@@ -361,9 +365,6 @@ bool SingleThreadProxy::doComposite()
 
         m_layerTreeHostImpl->animate(base::TimeTicks::Now(), base::Time::Now());
 
-        if (m_layerTreeHostImpl->settings().implSidePainting)
-          m_layerTreeHostImpl->manageTiles();
-
         // We guard prepareToDraw() with canDraw() because it always returns a valid frame, so can only
         // be used when such a frame is possible. Since drawLayers() depends on the result of
         // prepareToDraw(), it is guarded on canDraw() as well.