Update and extend context specialization.

src/compiler/js-context-specialization.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_JS_CONTEXT_SPECIALIZATION_H_
 #define V8_COMPILER_JS_CONTEXT_SPECIALIZATION_H_
 
 #include "src/compiler/graph-reducer.h"
 #include "src/compiler/js-graph.h"
 #include "src/contexts.h"
 #include "src/v8.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // Specializes a given JSGraph to a given context, potentially constant folding
-// some {LoadContext} nodes.
+// some {LoadContext} nodes or strength reducing some {StoreContext} nodes.
 class JSContextSpecializer {
  public:
   JSContextSpecializer(CompilationInfo* info, JSGraph* jsgraph, Node* context)
       : info_(info), jsgraph_(jsgraph), context_(context) {}
 
   void SpecializeToContext();
   Reduction ReduceJSLoadContext(Node* node);
+  Reduction ReduceJSStoreContext(Node* node);
 
  private:
   CompilationInfo* info_;
   JSGraph* jsgraph_;
   Node* context_;
 };
 }
 }
 }  // namespace v8::internal::compiler
 
 #endif  // V8_COMPILER_JS_CONTEXT_SPECIALIZATION_H_