Serialize external strings in the code serializer.

src/serialize.h

Index: src/serialize.h
diff --git a/src/serialize.h b/src/serialize.h
index 616f8f19c74ea44176b5574c3e9813bf6c27e264..6fa7a341e7a2de1589a9e886f56caec03a6efd65 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -439,12 +439,16 @@ class Serializer : public SerializerDeserializer {
     }
 
    private:
+    void SerializePrologue(int space, int size, Map* map);
+
     enum ReturnSkip { kCanReturnSkipInsteadOfSkipping, kIgnoringReturn };
     // This function outputs or skips the raw data between the last pointer and
     // up to the current position.  It optionally can just return the number of
     // bytes to skip instead of performing a skip instruction, in case the skip
     // can be merged into the next instruction.
     int OutputRawData(Address up_to, ReturnSkip return_skip = kIgnoringReturn);
+    // External strings are serialized in a way to resemble sequential strings.
+    void SerializeExternalString();
 
     Serializer* serializer_;
     HeapObject* object_;