Avoid two targeting phases in aura client-lib and EventProcessor.

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 039ec6daecec959a69aafabba001c85f4b746c5a..fe32d02553f75d0093e26e008247f90aa37267ae 100644
--- a/ui/aura/window_tree_host.cc
+++ b/ui/aura/window_tree_host.cc
@@ -260,8 +260,10 @@ void WindowTreeHost::CreateCompositor(const cc::FrameSinkId& frame_sink_id) {
     window()->Init(ui::LAYER_NOT_DRAWN);
     window()->set_host(this);
     window()->SetName("RootWindow");
-    window()->SetEventTargeter(
-        std::unique_ptr<ui::EventTargeter>(new WindowTargeter()));
+    if (Env::GetInstance()->mode() == Env::Mode::LOCAL) {

[sky, 2017/02/15 20:47:17]

Is it possible to remove this code and change Env to always create a
WindowTargeter?

[riajiang, 2017/02/16 00:34:08]

We are only creating a targeter for the root window in non-mus mode here because
we wanted to avoid walking all the way up to the root window just to use this
default event targeter when we try to find the farthest ancestor with a targeter
set in WindowEventDispatcher::GetRootForEvent. WDYT?

[sky, 2017/02/16 01:03:02]

The walking only happens in the mus case though, and I'm referring to the local
case. Maybe I missing something? What tree walking are you referring to?

Correct me if I'm wrong, but if you remove this code, and you make
WindowEventDispatcher always create the event_targeter_, then isn't that the
only changes that are needed? The local case won't do the tree walking as you
have it now.

[riajiang, 2017/02/16 19:10:35]

Oh I see, thanks for clarifying! You mean also getting the default targeter from
WindowEventDispatcher in EventProcessor for local case? I removed the code here
and changed WindowEventDispatcher to always create the targeter; EventProcessor
will then get the default targeter for the local case as well.

+      window()->SetEventTargeter(
+          std::unique_ptr<ui::EventTargeter>(new WindowTargeter()));
+    }
     dispatcher_.reset(new WindowEventDispatcher(this));
   }
 }