WIP: Eliminate event.target() usage from TrayEventFilter

mash/wm/window_manager_unittest.cc

 // Copyright 2015 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 <stdint.h>
 
 #include <memory>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 11 matching lines @@
 
 class WindowTreeDelegateImpl : public mus::WindowTreeDelegate {
  public:
   WindowTreeDelegateImpl() {}
   ~WindowTreeDelegateImpl() override {}
 
  private:
   // mus::WindowTreeDelegate:
   void OnEmbed(mus::Window* root) override {}
   void OnConnectionLost(mus::WindowTreeConnection* connection) override {}
-  void OnEventObserved(const ui::Event& event) override {}
+  void OnEventObserved(const ui::Event& event, mus::Window* target) override {}
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeDelegateImpl);
 };
 
 class WindowManagerTest : public shell::test::ShellTest {
  public:
   WindowManagerTest() : shell::test::ShellTest("exe:mash_unittests") {}
   ~WindowManagerTest() override {}
 
  private:
@@ skipping 108 matching lines @@
   mus::Window* top_level_window = connection->NewTopLevelWindow(nullptr);
   ASSERT_TRUE(top_level_window);
 
   observer.WaitUntilWindowCountReaches(1u);
   connection.reset();
   observer.WaitUntilWindowCountReaches(0u);
 }
 
 }  // namespace wm
 }  // namespace mash