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

ui/views/animation/bounds_animator_unittest.cc

Index: ui/views/animation/bounds_animator_unittest.cc
diff --git a/ui/views/animation/bounds_animator_unittest.cc b/ui/views/animation/bounds_animator_unittest.cc
index 2dbfc485a54ca165d9e3b63287cf6459c5bcddfb..c9431f88623280436161efb58fcc6ad3077b357e 100644
--- a/ui/views/animation/bounds_animator_unittest.cc
+++ b/ui/views/animation/bounds_animator_unittest.cc
@@ -129,8 +129,8 @@ TEST_F(BoundsAnimatorTest, AnimateViewTo) {
 
   // The parent should have been told to repaint as the animation progressed.
   // The resulting rect is the union of the original and target bounds.
-  target_bounds.Union(initial_bounds);
-  EXPECT_EQ(target_bounds, parent()->dirty_rect());
+  EXPECT_EQ(gfx::UnionRects(target_bounds, initial_bounds),
+            parent()->dirty_rect());
 }
 
 // Make sure an AnimationDelegate is deleted when canceled.