cc cleanup: simplify mask_uv_scale and MaskUVRect().

cc/layers/render_surface_impl.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/layers/render_surface_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 
@@ skipping 219 matching lines @@
   gfx::Transform owning_layer_draw_transform = owning_layer_->DrawTransform();
   if (mask_layer && mask_layer->DrawsContent() &&
       !mask_layer->bounds().IsEmpty()) {
     mask_layer->GetContentsResourceId(&mask_resource_id, &mask_texture_size);
     gfx::Vector2dF owning_layer_draw_scale =
         MathUtil::ComputeTransform2dScaleComponents(owning_layer_draw_transform,
                                                     1.f);
     gfx::SizeF unclipped_mask_target_size = gfx::ScaleSize(
         gfx::SizeF(owning_layer_->bounds()), owning_layer_draw_scale.x(),
         owning_layer_draw_scale.y());
-    mask_uv_scale = gfx::Vector2dF(
-        content_rect_.width() / unclipped_mask_target_size.width(),
-        content_rect_.height() / unclipped_mask_target_size.height());
+    mask_uv_scale = gfx::Vector2dF(1.0f / unclipped_mask_target_size.width(),
+                                   1.0f / unclipped_mask_target_size.height());
   }
 
   DCHECK(owning_layer_draw_transform.IsScale2d());
   gfx::Vector2dF owning_layer_to_target_scale =
       owning_layer_draw_transform.Scale2d();
 
   RenderPassDrawQuad* quad =
       render_pass->CreateAndAppendDrawQuad<RenderPassDrawQuad>();
   quad->SetNew(shared_quad_state, content_rect_, visible_layer_rect,
                render_pass_id, mask_resource_id, mask_uv_scale,
                mask_texture_size, owning_layer_->filters(),
                owning_layer_to_target_scale,
                owning_layer_->background_filters());
 }
 
 }  // namespace cc