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

tools/clang/rewrite_scoped_refptr/tests/test12-original.cc

Index: tools/clang/rewrite_scoped_refptr/tests/test12-original.cc
diff --git a/tools/clang/rewrite_scoped_refptr/tests/test12-original.cc b/tools/clang/rewrite_scoped_refptr/tests/test12-original.cc
index de4dd67258024f24cffb8d8387815e6daaa51391..33f1eb12ef14fec35eb29070b364043654e04a17 100644
--- a/tools/clang/rewrite_scoped_refptr/tests/test12-original.cc
+++ b/tools/clang/rewrite_scoped_refptr/tests/test12-original.cc
@@ -40,6 +40,7 @@ void TestsAScopedRefptr() {
   MyIter my_end(map.end());
   for (MyIter it = my_begin; it != my_end; ++it) {
     const Foo* item = NULL;
-    item = *it;
+    if (*it)
+      item = *it;
   }
 }