Introduce a hydrogen value for contexts, support context slot assignment.

src/hydrogen.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 805 matching lines @@
 
   HInstruction* BuildStoreKeyedFastElement(HValue* object,
                                            HValue* key,
                                            HValue* val,
                                            Expression* expr);
 
   HCompare* BuildSwitchCompare(HSubgraph* subgraph,
                                HValue* switch_value,
                                CaseClause* clause);
 
+  HValue* BuildContextChainWalk(Variable* var);
+
   void AddCheckConstantFunction(Call* expr,
                                 HValue* receiver,
                                 Handle<Map> receiver_map,
                                 bool smi_and_map_check);
 
 
   HBasicBlock* BuildTypeSwitch(ZoneMapList* maps,
                                ZoneList<HSubgraph*>* subgraphs,
                                HValue* receiver,
                                int join_id);
@@ skipping 230 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_