cc cleanup: simplify mask_uv_scale and MaskUVRect().

cc/quads/render_pass_draw_quad.cc

 // Copyright 2011 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 "cc/quads/render_pass_draw_quad.h"
 
 #include "base/trace_event/trace_event_argument.h"
 #include "base/values.h"
 #include "cc/base/math_util.h"
 #include "cc/debug/traced_value.h"
@@ skipping 55 matching lines @@
   resources.ids[kMaskResourceIdIndex] = mask_resource_id;
   resources.count = mask_resource_id ? 1 : 0;
   this->mask_uv_scale = mask_uv_scale;
   this->mask_texture_size = mask_texture_size;
   this->filters = filters;
   this->filters_scale = filters_scale;
   this->background_filters = background_filters;
 }
 
 gfx::RectF RenderPassDrawQuad::MaskUVRect() const {
-  gfx::RectF mask_uv_rect((mask_uv_scale.x() * rect.x()) / rect.width(),
-                          (mask_uv_scale.y() * rect.y()) / rect.height(),
-                          mask_uv_scale.x(),
-                          mask_uv_scale.y());
-  return mask_uv_rect;
+  return gfx::ScaleRect(gfx::RectF(rect), mask_uv_scale.x(), mask_uv_scale.y());
 }
 
 const RenderPassDrawQuad* RenderPassDrawQuad::MaterialCast(
     const DrawQuad* quad) {
   DCHECK_EQ(quad->material, DrawQuad::RENDER_PASS);
   return static_cast<const RenderPassDrawQuad*>(quad);
 }
 
 void RenderPassDrawQuad::ExtendValue(
     base::trace_event::TracedValue* value) const {
   TracedValue::SetIDRef(render_pass_id.AsTracingId(), value, "render_pass_id");
   value->SetInteger("mask_resource_id", resources.ids[kMaskResourceIdIndex]);
   MathUtil::AddToTracedValue("mask_texture_size", mask_texture_size, value);
   MathUtil::AddToTracedValue("mask_uv_scale", mask_uv_scale, value);
 
   value->BeginArray("filters");
   filters.AsValueInto(value);
   value->EndArray();
   MathUtil::AddToTracedValue("filters_scale", filters_scale, value);
 
   value->BeginDictionary("background_filters");
   background_filters.AsValueInto(value);
   value->EndDictionary();
 }
 
 }  // namespace cc