ui: Make gfx::Size::Scale() mutate the class. Add gfx::ScaleSize() similar to Rect/Point.

ui/gfx/canvas.cc

Index: ui/gfx/canvas.cc
diff --git a/ui/gfx/canvas.cc b/ui/gfx/canvas.cc
index bf41bc1357effecc63f8a7187d68ffc1d2149a75..eb11b379156b09e4441684cd2f8cebdd1d522a63 100644
--- a/ui/gfx/canvas.cc
+++ b/ui/gfx/canvas.cc
@@ -29,8 +29,8 @@ Canvas::Canvas(const gfx::Size& size,
       : scale_factor_(scale_factor),
         owned_canvas_(NULL),
         canvas_(NULL) {
-  gfx::Size pixel_size = gfx::ToFlooredSize(size.Scale(
-      ui::GetScaleFactorScale(scale_factor)));
+  gfx::Size pixel_size = gfx::ToFlooredSize(
+      gfx::ScaleSize(size, ui::GetScaleFactorScale(scale_factor)));
   owned_canvas_.reset(new skia::PlatformCanvas(pixel_size.width(),
                                                pixel_size.height(),
                                                is_opaque));
@@ -77,7 +77,7 @@ void Canvas::RecreateBackingCanvas(const gfx::Size& size,
                                    bool is_opaque) {
   scale_factor_ = scale_factor;
   gfx::Size pixel_size = gfx::ToFlooredSize(
-      size.Scale(ui::GetScaleFactorScale(scale_factor)));
+      gfx::ScaleSize(size, ui::GetScaleFactorScale(scale_factor)));
   owned_canvas_.reset(new skia::PlatformCanvas(pixel_size.width(),
                                                pixel_size.height(),
                                                is_opaque));