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

ui/gfx/rect_f.cc

 // 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.
 
 #include "ui/gfx/rect_f.h"
 
 #include "base/logging.h"
 #include "base/stringprintf.h"
 #include "ui/gfx/insets_f.h"
 #include "ui/gfx/rect_base_impl.h"
@@ skipping 24 matching lines @@
 }
 
 RectF::~RectF() {}
 
 std::string RectF::ToString() const {
   return base::StringPrintf("%s %s",
                             origin().ToString().c_str(),
                             size().ToString().c_str());
 }
 
+RectF IntersectRects(const RectF& a, const RectF& b) {
+  RectF result = a;
+  result.Intersect(b);
+  return result;
+}
+
+RectF UnionRects(const RectF& a, const RectF& b) {
+  RectF result = a;
+  result.Union(b);
+  return result;
+}
+
+RectF SubtractRects(const RectF& a, const RectF& b) {
+  RectF result = a;
+  result.Subtract(b);
+  return result;
+}
+
+RectF ScaleRect(const RectF& r, float x_scale, float y_scale) {
+  RectF result = r;
+  result.Scale(x_scale, y_scale);
+  return result;
+}
+
 }  // namespace gfx