[turbofan] Simply context specialization and fix for OSR.

src/compiler/js-context-specialization.cc

 // 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.
 
 #include "src/compiler/js-context-specialization.h"
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/js-operator.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 Reduction JSContextSpecializer::Reduce(Node* node) {
-  if (node == context_) {
-    Node* constant = jsgraph_->Constant(ctx_);
-    NodeProperties::ReplaceWithValue(node, constant);
-    return Replace(constant);
-  }
   if (node->opcode() == IrOpcode::kJSLoadContext) {
     return ReduceJSLoadContext(node);
   }
   if (node->opcode() == IrOpcode::kJSStoreContext) {
     return ReduceJSStoreContext(node);
   }
   return NoChange();
 }
 
 
@@ skipping 75 matching lines @@
   Handle<Object> new_context_handle =
       Handle<Object>(context, jsgraph_->isolate());
   node->ReplaceInput(0, jsgraph_->Constant(new_context_handle));
 
   return Changed(node);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8