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

ash/tooltips/tooltip_controller_unittest.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/display/display_controller.h"
 #include "ash/shell.h"
 #include "ash/test/ash_test_base.h"
 #include "ash/tooltips/tooltip_controller.h"
 #include "ash/wm/cursor_manager.h"
 #include "base/utf_string_conversions.h"
@@ skipping 54 matching lines @@
 void AddViewToWidgetAndResize(views::Widget* widget, views::View* view) {
   if (!widget->GetContentsView()) {
     views::View* contents_view = new views::View;
     widget->SetContentsView(contents_view);
   }
 
   views::View* contents_view = widget->GetContentsView();
   contents_view->AddChildView(view);
   view->SetBounds(contents_view->width(), 0, 100, 100);
   gfx::Rect contents_view_bounds = contents_view->bounds();
-  contents_view_bounds = contents_view_bounds.Union(view->bounds());
+  contents_view_bounds.Union(view->bounds());
   contents_view->SetBoundsRect(contents_view_bounds);
   widget->SetBounds(gfx::Rect(widget->GetWindowBoundsInScreen().origin(),
                               contents_view_bounds.size()));
 }
 
 ash::internal::TooltipController* GetController() {
   return static_cast<ash::internal::TooltipController*>(
       aura::client::GetTooltipClient(Shell::GetPrimaryRootWindow()));
 }
 
@@ skipping 426 matching lines @@
   // be able to show tooltips on the primary display.
   aura::test::EventGenerator generator1(root_windows[0]);
   generator1.MoveMouseRelativeTo(widget1->GetNativeView(),
                                  view1->bounds().CenterPoint());
   FireTooltipTimer();
   EXPECT_TRUE(IsTooltipVisible());
 }
 
 }  // namespace test
 }  // namespace ash