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

ui/gfx/rect_f.h

 // 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.
 
 #ifndef UI_GFX_RECT_F_H_
 #define UI_GFX_RECT_F_H_
 
 #include <string>
 
 #include "ui/gfx/point_f.h"
@@ skipping 31 matching lines @@
 };
 
 inline bool operator==(const RectF& lhs, const RectF& rhs) {
   return lhs.origin() == rhs.origin() && lhs.size() == rhs.size();
 }
 
 inline bool operator!=(const RectF& lhs, const RectF& rhs) {
   return !(lhs == rhs);
 }
 
+UI_EXPORT RectF IntersectRects(const RectF& a, const RectF& b);
+UI_EXPORT RectF UnionRects(const RectF& a, const RectF& b);
+UI_EXPORT RectF SubtractRects(const RectF& a, const RectF& b);
+UI_EXPORT RectF ScaleRect(const RectF& r, float x_scale, float y_scale);
+
+inline RectF ScaleRect(const RectF& r, float scale) {
+  return ScaleRect(r, scale, scale);
+}
+
 #if !defined(COMPILER_MSVC)
 extern template class RectBase<RectF, PointF, SizeF, InsetsF, float>;
 #endif
 
 }  // namespace gfx
 
 #endif  // UI_GFX_RECT_F_H_