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

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

Index: tools/clang/rewrite_scoped_refptr/tests/test12-expected.cc
diff --git a/tools/clang/rewrite_scoped_refptr/tests/test12-expected.cc b/tools/clang/rewrite_scoped_refptr/tests/test12-expected.cc
index 37f350c947b27eaac9be0cec6e0423526b63b718..fdaa80e18fe5f403392c7e497d2417bbe64aa3e6 100644
--- a/tools/clang/rewrite_scoped_refptr/tests/test12-expected.cc
+++ b/tools/clang/rewrite_scoped_refptr/tests/test12-expected.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->get();
+    if (it->get())
+      item = it->get();
   }
 }