Snapshots: Add --extra-code flag to mksnapshot which lets you specify a file

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 11803)
+++ src/heap.cc	(working copy)
@@ -2822,7 +2822,7 @@
   // The idea is to have a small number string cache in the snapshot to keep
   // boot-time memory usage down.  If we expand the number string cache already
   // while creating the snapshot then that didn't work out.
-  ASSERT(!Serializer::enabled());
+  ASSERT(!Serializer::enabled() || FLAG_extra_code != NULL);
   MaybeObject* maybe_obj =
       AllocateFixedArray(FullSizeNumberStringCacheLength(), TENURED);
   Object* new_cache;