WIP: Eliminate event.target() usage from TrayEventFilter

components/mus/demo/mus_demo.cc

 // Copyright 2016 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 "components/mus/demo/mus_demo.h"
 
 #include "base/time/time.h"
 #include "components/bitmap_uploader/bitmap_uploader.h"
 #include "components/mus/public/cpp/window_tree_host_factory.h"
 #include "third_party/skia/include/core/SkCanvas.h"
@@ skipping 72 matching lines @@
   timer_.Start(FROM_HERE, base::TimeDelta::FromMilliseconds(kFrameDelay),
                base::Bind(&MusDemo::DrawFrame, base::Unretained(this)));
 }
 
 void MusDemo::OnUnembed(mus::Window* root) {}
 
 void MusDemo::OnConnectionLost(mus::WindowTreeConnection* connection) {
   timer_.Stop();
 }
 
-void MusDemo::OnEventObserved(const ui::Event& event) {}
+void MusDemo::OnEventObserved(const ui::Event& event, mus::Window* target) {}
 
 void MusDemo::SetWindowManagerClient(mus::WindowManagerClient* client) {}
 
 bool MusDemo::OnWmSetBounds(mus::Window* window, gfx::Rect* bounds) {
   return true;
 }
 
 bool MusDemo::OnWmSetProperty(mus::Window* window,
                               const std::string& name,
                               std::unique_ptr<std::vector<uint8_t>>* new_data) {
@@ skipping 48 matching lines @@
   std::unique_ptr<std::vector<unsigned char>> data(
       new std::vector<unsigned char>(addr, addr + bytes));
   bitmap_.unlockPixels();
 
   // Send frame to MUS via BitmapUploader.
   uploader_->SetBitmap(bounds.width(), bounds.height(), std::move(data),
                        bitmap_uploader::BitmapUploader::BGRA);
 }
 
 }  // namespace mus_demo