Make gfx::Rect class operations consistently mutate the class they are called on.

ash/launcher/launcher_view.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 "ash/launcher/launcher_view.h"
 
 #include <algorithm>
 
 #include "ash/launcher/app_list_button.h"
 #include "ash/launcher/launcher_button.h"
@@ skipping 687 matching lines @@
     views::View* child = child_at(i);
     if (child == overflow_button_)
       continue;
 
     // The tooltip shouldn't show over the app-list window.
     if (child == GetAppListButtonView() &&
         Shell::GetInstance()->GetAppListWindow())
       continue;
 
     gfx::Rect child_bounds = child->GetMirroredBounds();
-    active_bounds = active_bounds.Union(child_bounds);
+    active_bounds.Union(child_bounds);
   }
 
   return !active_bounds.Contains(cursor_location);
 }
 
 int LauncherView::CancelDrag(int modified_index) {
   if (!drag_view_)
     return modified_index;
   bool was_dragging = dragging();
   int drag_view_index = view_model_->GetIndexOfView(drag_view_);
@@ skipping 354 matching lines @@
   FOR_EACH_OBSERVER(LauncherIconObserver, observers_,
                     OnLauncherIconPositionsChanged());
   PreferredSizeChanged();
 }
 
 void LauncherView::OnBoundsAnimatorDone(views::BoundsAnimator* animator) {
 }
 
 }  // namespace internal
 }  // namespace ash