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

ui/events/event_processor.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/event_processor.h"
 
 #include "ui/events/event_target.h"
 #include "ui/events/event_targeter.h"
 
 namespace ui {
 
 EventDispatchDetails EventProcessor::OnEventFromSource(Event* event) {
-  EventTarget* root = GetRootTarget();
-  CHECK(root);
-  EventTargeter* targeter = root->GetEventTargeter();
-  CHECK(targeter);
-
   // If |event| is in the process of being dispatched or has already been
   // dispatched, then dispatch a copy of the event instead.
   bool dispatch_original_event = event->phase() == EP_PREDISPATCH;
   Event* event_to_dispatch = event;
   std::unique_ptr<Event> event_copy;
   if (!dispatch_original_event) {
     event_copy = Event::Clone(*event);
     event_to_dispatch = event_copy.get();
   }
 
   OnEventProcessingStarted(event_to_dispatch);
-  EventTarget* target = NULL;
-  if (!event_to_dispatch->handled())
-    target = targeter->FindTargetForEvent(root, event_to_dispatch);
+  EventTarget* target = event->target();
+  EventTargeter* targeter = nullptr;
+  if (!event_to_dispatch->handled()) {
+    EventTarget* root = GetRootForEvent(event_to_dispatch);
+    DCHECK(root);
+    targeter = root->GetEventTargeter();
+    if (!targeter) {
+      targeter = GetDefaultEventTargeter();
+      if (!target)
+        target = targeter->FindTargetForEvent(root, event_to_dispatch);
+    } else {
+      target = targeter->FindTargetForEvent(root, event_to_dispatch);

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

This duplicates line 33. I think it would be easier if you closed the if started
on line 30 at line 32 and moved the if the starts on line 32 after it, e.g.
if (!targeter)
  targeter = ...
if (!target)
  target = ...

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

I'm not sure if I understood this. There's a case when we have both target and
targeter (mus-ws sets the target but ash wanted to use that custom targeter), we
do want to update the target using this custom targeter in that case?

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

Ah, I see it now. Thanks.

+    }
+    DCHECK(targeter);
+  }
 
   EventDispatchDetails details;
   while (target) {
     details = DispatchEvent(target, event_to_dispatch);
 
     if (!dispatch_original_event) {
       if (event_to_dispatch->stopped_propagation())
         event->StopPropagation();
       else if (event_to_dispatch->handled())
         event->SetHandled();
@@ skipping 12 matching lines @@
   return details;
 }
 
 void EventProcessor::OnEventProcessingStarted(Event* event) {
 }
 
 void EventProcessor::OnEventProcessingFinished(Event* event) {
 }
 
 }  // namespace ui