ui: Add methods to Rect classes to get points at each of the rect's corners.

ui/gfx/rect_base.h

Index: ui/gfx/rect_base.h
diff --git a/ui/gfx/rect_base.h b/ui/gfx/rect_base.h
index 3ad12c8b245b2cccc0e81706af8f4123083009d0..1be30400d6e91e9740bafb3d79e7df535bc40d3e 100644
--- a/ui/gfx/rect_base.h
+++ b/ui/gfx/rect_base.h
@@ -47,6 +47,10 @@ class UI_EXPORT RectBase {
   Type right() const { return x() + width(); }
   Type bottom() const { return y() + height(); }
 
+  PointClass top_right() const { return PointClass(right(), y()); }
+  PointClass bottom_left() const { return PointClass(x(), bottom()); }
+  PointClass bottom_right() const { return PointClass(right(), bottom()); }
+
   VectorClass OffsetFromOrigin() const {
     return VectorClass(x(), y());
   }