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

src/isolate.h

Index: src/isolate.h
===================================================================
--- src/isolate.h	(revision 11803)
+++ src/isolate.h	(working copy)
@@ -307,7 +307,6 @@
 
 #define ISOLATE_INIT_ARRAY_LIST(V)                                             \
   /* SerializerDeserializer state. */                                          \
-  V(Object*, serialize_partial_snapshot_cache, kPartialSnapshotCacheCapacity)  \
   V(int, jsregexp_static_offsets_vector, kJSRegexpStaticOffsetsVectorSize)     \
   V(int, bad_char_shift_table, kUC16AlphabetSize)                              \
   V(int, good_suffix_shift_table, (kBMMaxShift + 1))                           \
@@ -320,6 +319,8 @@
 #define ISOLATE_INIT_LIST(V)                                                   \
   /* SerializerDeserializer state. */                                          \
   V(int, serialize_partial_snapshot_cache_length, 0)                           \
+  V(int, serialize_partial_snapshot_cache_capacity, 0)                         \
+  V(Object**, serialize_partial_snapshot_cache, NULL)                          \
   /* Assembler state. */                                                       \
   /* A previously allocated buffer of kMinimalBufferSize bytes, or NULL. */    \
   V(byte*, assembler_spare_buffer, NULL)                                       \
@@ -610,6 +611,9 @@
         (exception != heap()->termination_exception());
   }
 
+  // Serializer.
+  void PushToPartialSnapshotCache(Object* obj);
+
   // JS execution stack (see frames.h).
   static Address c_entry_fp(ThreadLocalTop* thread) {
     return thread->c_entry_fp_;