Move visual rect unioning between paired items to cc::DisplayItemList.

ui/compositor/compositing_recorder.cc

 // Copyright 2015 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/compositor/compositing_recorder.h"
 
 #include "cc/playback/compositing_display_item.h"
 #include "cc/playback/display_item_list.h"
 #include "ui/compositor/paint_context.h"
 #include "ui/gfx/canvas.h"
 
 namespace ui {
 
 CompositingRecorder::CompositingRecorder(const PaintContext& context,
-                                         const gfx::Size& size_in_context,
                                          uint8_t alpha,
                                          bool lcd_text_requires_opaque_layer)
     : context_(context),
-      bounds_in_layer_(context.ToLayerSpaceBounds(size_in_context)),
       saved_(alpha < 255) {
   if (!saved_)
     return;
 
-  context_.list_->CreateAndAppendItem<cc::CompositingDisplayItem>(
-      bounds_in_layer_, alpha, SkXfermode::kSrcOver_Mode,
-      nullptr /* no bounds */, nullptr /* no color filter */,
-      lcd_text_requires_opaque_layer);
+  context_.list_->CreateAndAppendPairedBeginItem<cc::CompositingDisplayItem>(
+      alpha, SkXfermode::kSrcOver_Mode, nullptr /* no bounds */,
+      nullptr /* no color filter */, lcd_text_requires_opaque_layer);
 }
 
 CompositingRecorder::~CompositingRecorder() {
   if (!saved_)
     return;
 
-  context_.list_->CreateAndAppendItem<cc::EndCompositingDisplayItem>(
-      bounds_in_layer_);
+  context_.list_->CreateAndAppendPairedEndItem<cc::EndCompositingDisplayItem>();
 }
 
 }  // namespace ui