[turbofan] Move context specialization into JSContextSpecializer.

src/compiler/js-context-specialization.cc

Index: src/compiler/js-context-specialization.cc
diff --git a/src/compiler/js-context-specialization.cc b/src/compiler/js-context-specialization.cc
index bb44f5928bb0efe87537c116b605189550f6ea49..b837a6277310784d4ee0ccf98f361dd2f282026d 100644
--- a/src/compiler/js-context-specialization.cc
+++ b/src/compiler/js-context-specialization.cc
@@ -16,11 +16,26 @@ namespace internal {
 namespace compiler {
 
 Reduction JSContextSpecializer::Reduce(Node* node) {
-  if (node->opcode() == IrOpcode::kJSLoadContext) {
-    return ReduceJSLoadContext(node);
+  switch (node->opcode()) {
+    case IrOpcode::kParameter:
+      return ReduceParameter(node);
+    case IrOpcode::kJSLoadContext:
+      return ReduceJSLoadContext(node);
+    case IrOpcode::kJSStoreContext:
+      return ReduceJSStoreContext(node);
+    default:
+      break;
   }
-  if (node->opcode() == IrOpcode::kJSStoreContext) {
-    return ReduceJSStoreContext(node);
+  return NoChange();
+}
+
+
+Reduction JSContextSpecializer::ReduceParameter(Node* node) {
+  DCHECK_EQ(IrOpcode::kParameter, node->opcode());
+  Handle<Context> context_constant;
+  if (ParameterIndexOf(node->op()) == context_index() &&
+      context().ToHandle(&context_constant)) {
+    return Replace(jsgraph()->Constant(context_constant));
   }
   return NoChange();
 }