Reapply r9673 "Scope tree serialization and ScopeIterator cleanup."

src/contexts.h

 // Copyright 2011 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 176 matching lines @@
     return reinterpret_cast<Context*>(context);
   }
 
   // The default context slot layout; indices are FixedArray slot indices.
   enum {
     // These slots are in all contexts.
     CLOSURE_INDEX,
     PREVIOUS_INDEX,
     // The extension slot is used for either the global object (in global
     // contexts), eval extension object (function contexts), subject of with
-    // (with contexts), or the variable name (catch contexts).
+    // (with contexts), or the variable name (catch contexts), the serialized
+    // scope info (block contexts).
     EXTENSION_INDEX,
     GLOBAL_INDEX,
     MIN_CONTEXT_SLOTS,
 
     // This slot holds the thrown value in catch contexts.
     THROWN_OBJECT_INDEX = MIN_CONTEXT_SLOTS,
 
     // These slots are only in global contexts.
     GLOBAL_PROXY_INDEX = MIN_CONTEXT_SLOTS,
     SECURITY_TOKEN_INDEX,
@@ skipping 202 matching lines @@
 #ifdef DEBUG
   // Bootstrapping-aware type checks.
   static bool IsBootstrappingOrContext(Object* object);
   static bool IsBootstrappingOrGlobalObject(Object* object);
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONTEXTS_H_