Do not dump user source code in the code serializer.

test/cctest/test-serialize.cc

Index: test/cctest/test-serialize.cc
diff --git a/test/cctest/test-serialize.cc b/test/cctest/test-serialize.cc
index 7d228cabfbcbb3105d0421687415bacffcf2702c..f025d8f26c152d7952e2043b24a1ea590a13ec32 100644
--- a/test/cctest/test-serialize.cc
+++ b/test/cctest/test-serialize.cc
@@ -707,6 +707,8 @@ TEST(SerializeToplevelOnePlusOne) {
                               &cache, CONSUME_CACHED_DATA, NOT_NATIVES_CODE);
 
   CHECK_NE(*orig, *copy);
+  CHECK(Script::cast(copy->script())->source() == *source2_string);
+
   Handle<JSFunction> copy_fun =
       isolate->factory()->NewFunctionFromSharedFunctionInfo(
           copy, isolate->native_context());
@@ -758,6 +760,8 @@ TEST(SerializeToplevelInternalizedString) {
                               Handle<Context>(isolate->native_context()), NULL,
                               &cache, CONSUME_CACHED_DATA, NOT_NATIVES_CODE);
   CHECK_NE(*orig, *copy);
+  CHECK(Script::cast(copy->script())->source() == *source2_string);
+
   Handle<JSFunction> copy_fun =
       isolate->factory()->NewFunctionFromSharedFunctionInfo(
           copy, isolate->native_context());