Introduce global contexts to represent lexical global scope(s).

src/contexts.h

 // Copyright 2012 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 172 matching lines @@
 //                function contexts, and non-NULL for 'with' contexts.
 //                Used to implement the 'with' statement.
 //
 // [ extension ]  A pointer to an extension JSObject, or NULL. Used to
 //                implement 'with' statements and dynamic declarations
 //                (through 'eval'). The object in a 'with' statement is
 //                stored in the extension slot of a 'with' context.
 //                Dynamically declared variables/functions are also added
 //                to lazily allocated extension object. Context::Lookup
 //                searches the extension object for properties.
-//                For block contexts, contains the respective ScopeInfo.
+//                For global and block contexts, contains the respective
+//                ScopeInfo.
 //                For module contexts, points back to the respective JSModule.
 //
 // [ global_object ]  A pointer to the global object. Provided for quick
 //                access to the global object from inside the code (since
 //                we always have a context pointer).
 //
 // In addition, function contexts may have statically allocated context slots
 // to store local variables/functions that are accessed from inner functions
 // (via static context addresses) or through 'eval' (dynamic context lookups).
 // Finally, the native context contains additional slots for fast access to
@@ skipping 152 matching lines @@
     return map == map->GetHeap()->with_context_map();
   }
   bool IsBlockContext() {
     Map* map = this->map();
     return map == map->GetHeap()->block_context_map();
   }
   bool IsModuleContext() {
     Map* map = this->map();
     return map == map->GetHeap()->module_context_map();
   }
+  bool IsGlobalContext() {
+    Map* map = this->map();
+    return map == map->GetHeap()->global_context_map();
+  }
 
   // Tells whether the native context is marked with out of memory.
   inline bool has_out_of_memory();
 
   // Mark the native context with out of memory.
   inline void mark_out_of_memory();
 
   // A native context hold a list of all functions which have been optimized.
   void AddOptimizedFunction(JSFunction* function);
   void RemoveOptimizedFunction(JSFunction* function);
@@ skipping 58 matching lines @@
 #ifdef DEBUG
   // Bootstrapping-aware type checks.
   static bool IsBootstrappingOrValidParentContext(Object* object, Context* kid);
   static bool IsBootstrappingOrGlobalObject(Object* object);
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONTEXTS_H_