cc: Remove use of PassAs() and constructor-casting with scoped_ptr.

cc/resources/ui_resource_request.cc

 // Copyright 2013 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/resources/ui_resource_request.h"
 
 namespace cc {
 
 UIResourceRequest::UIResourceRequest(UIResourceRequestType type,
                                      UIResourceId id)
     : type_(type), id_(id) {}
 
 UIResourceRequest::UIResourceRequest(UIResourceRequestType type,
                                      UIResourceId id,
                                      const UIResourceBitmap& bitmap)
     : type_(type), id_(id), bitmap_(new UIResourceBitmap(bitmap)) {}
 
 UIResourceRequest::UIResourceRequest(const UIResourceRequest& request) {
   (*this) = request;
 }
 
 UIResourceRequest& UIResourceRequest::operator=(
     const UIResourceRequest& request) {
   type_ = request.type_;
   id_ = request.id_;
   if (request.bitmap_) {
     bitmap_ = make_scoped_ptr(new UIResourceBitmap(*request.bitmap_.get()));
   } else {
-    bitmap_.reset();
+    bitmap_ = nullptr;
   }
 
   return *this;
 }
 
 UIResourceRequest::~UIResourceRequest() {}
 
 }  // namespace cc