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

ash/launcher/launcher_view_unittest.cc

Index: ash/launcher/launcher_view_unittest.cc
diff --git a/ash/launcher/launcher_view_unittest.cc b/ash/launcher/launcher_view_unittest.cc
index 3e1e80660add82dde5513f6b6394d0b53c6de39f..468e8f90084654723b5192595bddfa11253627b6 100644
--- a/ash/launcher/launcher_view_unittest.cc
+++ b/ash/launcher/launcher_view_unittest.cc
@@ -645,9 +645,8 @@ TEST_F(LauncherViewTest, ShouldHideTooltipTest) {
   gfx::Rect app_button_rect = GetButtonByID(app_button_id)->GetMirroredBounds();
   gfx::Rect tab_button_rect = GetButtonByID(tab_button_id)->GetMirroredBounds();
   ASSERT_FALSE(app_button_rect.Intersects(tab_button_rect));
-  gfx::Rect union_rect = app_button_rect;
-  union_rect.Union(tab_button_rect);
-  EXPECT_FALSE(launcher_view_->ShouldHideTooltip(union_rect.CenterPoint()));
+  EXPECT_FALSE(launcher_view_->ShouldHideTooltip(
+      gfx::UnionRects(app_button_rect, tab_button_rect).CenterPoint()));
 
   // The tooltip should hide if it's outside of all buttons.
   gfx::Rect all_area;