Add --disable-compositor-touch-hit-testing flag

Plumb the flag to blink and the compositor.
Disable by default in Android webview for now.

Depends on blink CL: https://src.chromium.org/viewvc/blink?view=rev&revision=158956

BUG=303945

Review URL: https://codereview.chromium.org/25904004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227511 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index a224224..d8ca19b 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -426,6 +426,8 @@
 }
 
 bool LayerTreeHostImpl::HaveTouchEventHandlersAt(gfx::Point viewport_point) {
+  if (!settings_.touch_hit_testing)
+    return true;
   if (!EnsureRenderSurfaceLayerList())
     return false;