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

ui/gfx/image/image_skia_operations.cc

Index: ui/gfx/image/image_skia_operations.cc
diff --git a/ui/gfx/image/image_skia_operations.cc b/ui/gfx/image/image_skia_operations.cc
index 0dcc4d81955f4f4cebd38e4c68074580efa172f3..708f55037292a001530a2ddf293bd842c2fa168a 100644
--- a/ui/gfx/image/image_skia_operations.cc
+++ b/ui/gfx/image/image_skia_operations.cc
@@ -288,11 +288,8 @@ class ExtractSubsetImageSource: public gfx::ImageSkiaSource {
   // gfx::ImageSkiaSource overrides:
   virtual ImageSkiaRep GetImageForScale(ui::ScaleFactor scale_factor) OVERRIDE {
     ImageSkiaRep image_rep = image_.GetRepresentation(scale_factor);
-    gfx::RectF scaled_subset_bounds = subset_bounds_;
-    scaled_subset_bounds.Scale(
-        ui::GetScaleFactorScale(image_rep.scale_factor()));
-    SkIRect subset_bounds_in_pixel = RectToSkIRect(
-        ToEnclosingRect(scaled_subset_bounds));
+    SkIRect subset_bounds_in_pixel = RectToSkIRect(ToEnclosingRect(gfx::Scale(
+        subset_bounds_, ui::GetScaleFactorScale(image_rep.scale_factor()))));
     SkBitmap dst;
     bool success = image_rep.sk_bitmap().extractSubset(&dst,
                                                        subset_bounds_in_pixel);
@@ -432,8 +429,8 @@ ImageSkia ImageSkiaOperations::CreateButtonBackground(SkColor color,
 // static
 ImageSkia ImageSkiaOperations::ExtractSubset(const ImageSkia& image,
                                              const Rect& subset_bounds) {
-  gfx::Rect clipped_bounds = subset_bounds;
-  clipped_bounds.Intersect(gfx::Rect(image.size()));
+  gfx::Rect clipped_bounds =
+      gfx::Intersection(subset_bounds, gfx::Rect(image.size()));
   if (image.isNull() || clipped_bounds.IsEmpty()) {
     return ImageSkia();
   }