linux and chromeos: Turn on -Wunused-const-variable.

ui/views/widget/widget_interactive_uitest.cc

 // Copyright (c) 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 "base/basictypes.h"
 #include "base/bind.h"
 #include "base/run_loop.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/views/test/widget_test.h"
 #include "ui/views/widget/widget.h"
@@ skipping 662 matching lines @@
   MouseEventTrackingWidget() : got_mouse_event_(false) {}
   virtual ~MouseEventTrackingWidget() {}
 
   bool GetAndClearGotMouseEvent() {
     bool value = got_mouse_event_;
     got_mouse_event_ = false;
     return value;
   }
 
   // Widget:
-  virtual void OnMouseEvent(ui::MouseEvent* event) {
+  virtual void OnMouseEvent(ui::MouseEvent* event) OVERRIDE {
     got_mouse_event_ = true;
     Widget::OnMouseEvent(event);
   }
 
  private:
   bool got_mouse_event_;
 
   DISALLOW_COPY_AND_ASSIGN(MouseEventTrackingWidget);
 };
 
@@ skipping 32 matching lines @@
   static_cast<aura::RootWindowHostDelegate*>(
       widget1.GetNativeWindow()->GetRootWindow())->OnHostMouseEvent(
           &mouse_event);
   EXPECT_TRUE(widget1.GetAndClearGotMouseEvent());
   EXPECT_FALSE(widget2.GetAndClearGotMouseEvent());
 }
 #endif
 
 }  // namespace test
 }  // namespace views