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

ui/views/widget/root_view.cc

Index: ui/views/widget/root_view.cc
diff --git a/ui/views/widget/root_view.cc b/ui/views/widget/root_view.cc
index ec6dc50ced2a08e778497b1a818a2db6170a7be0..1cb6bfc7514b6beadbb4b242ff27b3acf7574233 100644
--- a/ui/views/widget/root_view.cc
+++ b/ui/views/widget/root_view.cc
@@ -191,8 +191,7 @@ void RootView::SchedulePaintInRect(const gfx::Rect& rect) {
     layer()->SchedulePaint(rect);
   } else {
     gfx::Rect xrect = ConvertRectToParent(rect);
-    gfx::Rect invalid_rect = GetLocalBounds();
-    invalid_rect.Intersect(xrect);
+    gfx::Rect invalid_rect = gfx::Intersection(GetLocalBounds(), xrect);
     if (!invalid_rect.IsEmpty())
       widget_->SchedulePaintInRect(invalid_rect);
   }