Add non-member non-mutating methods for common gfx::Rect operations.

ui/gfx/screen_gtk.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/gfx/screen.h"
 
 #include <gdk/gdkx.h>
 #include <gtk/gtk.h>
 
 #include "base/logging.h"
@@ skipping 139 matching lines @@
     return GetPrimaryDisplay();
   }
 
   // Returns the primary display.
   virtual gfx::Display GetPrimaryDisplay() const OVERRIDE {
     gfx::Rect bounds = NativePrimaryMonitorBounds();
     // TODO(oshima): Implement ID and Observer.
     gfx::Display display(0, bounds);
     gfx::Rect rect;
     if (GetScreenWorkArea(&rect)) {
-      bounds.Intersect(rect);
-      display.set_work_area(bounds);
+      display.set_work_area(gfx::IntersectRects(rect, bounds));
     } else {
       // Return the best we've got.
       display.set_work_area(bounds);
     }
     return display;
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ScreenGtk);
 };
 
 }  // namespace
 
 namespace gfx {
 
 Screen* CreateNativeScreen() {
   return new ScreenGtk;
 }
 
 }  // namespace gfx