Implement rewrite logic for assigning a temporary scoped_refptr to T*.

tools/clang/rewrite_scoped_refptr/tests/temp-assigned-to-raw-var-expected.cc

 // Copyright (c) 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 "scoped_refptr.h"
 
 struct Foo {
   int dummy;
 };
 
 // Case 2: An example of an unsafe conversion, where the scoped_refptr<> is
 // returned as a temporary, and as such both it and its object are only valid
 // for the duration of the full expression.
 scoped_refptr<Foo> GetBuggyFoo() {
   return new Foo;
 }
 void UseBuggyFoo() {
-  Foo* unsafe = GetBuggyFoo();
+  scoped_refptr<Foo> unsafe = GetBuggyFoo();
 }