Relanding the EventTarget fixes for Aura (Ash) as the previous attempt was reverted due to interact…

ui/aura/root_window_unittest.cc

 // Copyright (c) 2012 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/aura/root_window.h"
 
 #include <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/aura/client/event_client.h"
@@ skipping 318 matching lines @@
     return root_window_->GetChildById(kNonLockWindowId);
   }
 
  private:
   // Overridden from client::EventClient:
   virtual bool CanProcessEventsWithinSubtree(
       const Window* window) const OVERRIDE {
     return lock_ ? GetLockWindow()->Contains(window) : true;
   }
 
+  virtual ui::EventTarget* GetToplevelEventTarget() OVERRIDE {
+    return NULL;
+  }
+
   RootWindow* root_window_;
   bool lock_;
 
   DISALLOW_COPY_AND_ASSIGN(TestEventClient);
 };
 
 }  // namespace
 
 TEST_F(RootWindowTest, CanProcessEventsWithinSubtree) {
   TestEventClient client(root_window());
@@ skipping 425 matching lines @@
 TEST_F(RootWindowTest, GestureRecognizerResetsTargetWhenParentHides) {
   scoped_ptr<Window> w1(CreateWindow(1, root_window(), NULL));
   DetachesParentOnTapDelegate delegate;
   scoped_ptr<Window> parent(CreateWindow(22, w1.get(), NULL));
   Window* child = CreateWindow(11, parent.get(), &delegate);
   test::EventGenerator generator(root_window(), child);
   generator.GestureTapAt(gfx::Point(40, 40));
 }
 
 }  // namespace aura