Do not dump user source code in the code serializer.

test/cctest/test-serialize.cc

 // Copyright 2007-2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 689 matching lines @@
                               &cache, PRODUCE_CACHED_DATA, NOT_NATIVES_CODE);
 
   int builtins_count = CountBuiltins();
 
   Handle<SharedFunctionInfo> copy =
       Compiler::CompileScript(source2_string, Handle<String>(), 0, 0, false,
                               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());
   Handle<JSObject> global(isolate->context()->global_object());
   Handle<Object> copy_result =
       Execution::Call(isolate, copy_fun, global, 0, NULL).ToHandleChecked();
   CHECK_EQ(2, Handle<Smi>::cast(copy_result)->value());
 
   CHECK_EQ(builtins_count, CountBuiltins());
 
@@ skipping 31 matching lines @@
       Execution::Call(isolate, orig_fun, global, 0, NULL).ToHandleChecked();
   CHECK(orig_result->IsInternalizedString());
 
   int builtins_count = CountBuiltins();
 
   Handle<SharedFunctionInfo> copy =
       Compiler::CompileScript(source2_string, Handle<String>(), 0, 0, false,
                               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());
   CHECK_NE(*orig_fun, *copy_fun);
   Handle<Object> copy_result =
       Execution::Call(isolate, copy_fun, global, 0, NULL).ToHandleChecked();
   CHECK(orig_result.is_identical_to(copy_result));
   Handle<String> expected =
       isolate->factory()->NewStringFromAsciiChecked("string1");
 
   CHECK(Handle<String>::cast(copy_result)->Equals(*expected));
   CHECK_EQ(builtins_count, CountBuiltins());
 
   delete cache;
 }