Create pre-frozen change records for Object.observe

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 745ba65347e4303ce15e96eacf1feda004c2d169..ec9c25721213f36ec87672334ba320b2ea4b3e68 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -164,6 +164,8 @@ enum BindingFlags {
   V(PROXY_ENUMERATE_INDEX, JSFunction, proxy_enumerate) \
   V(OBSERVERS_NOTIFY_CHANGE_INDEX, JSFunction, observers_notify_change) \
   V(OBSERVERS_DELIVER_CHANGES_INDEX, JSFunction, observers_deliver_changes) \
+  V(CHANGE_RECORD_MAP_INDEX, Map, change_record_map) \
+  V(CHANGE_RECORD_OLDVALUE_MAP_INDEX, Map, change_record_oldvalue_map) \
   V(RANDOM_SEED_INDEX, ByteArray, random_seed)
 
 // JSFunctions are pairs (context, function code), sometimes also called
@@ -293,6 +295,8 @@ class Context: public FixedArray {
     PROXY_ENUMERATE_INDEX,
     OBSERVERS_NOTIFY_CHANGE_INDEX,
     OBSERVERS_DELIVER_CHANGES_INDEX,
+    CHANGE_RECORD_MAP_INDEX,
+    CHANGE_RECORD_OLDVALUE_MAP_INDEX,
     RANDOM_SEED_INDEX,
 
     // Properties from here are treated as weak references by the full GC.