Turn FastNewContextStub into a HydrogenCodeStub.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index a61ec90c304c67e82267509204a13803a02c7503..ce506ce7746e94443d773e3b736dbe2bd8ccd8d4 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -8869,7 +8869,6 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_NewGlobalContext) {
 
   ASSERT(function->context() == isolate->context());
   ASSERT(function->context()->global_object() == result->global_object());
-  isolate->set_context(result);
   result->global_object()->set_global_context(result);
 
   return result;  // non-failure
@@ -8882,14 +8881,7 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_NewFunctionContext) {
 
   CONVERT_ARG_CHECKED(JSFunction, function, 0);
   int length = function->shared()->scope_info()->ContextLength();
-  Context* result;
-  MaybeObject* maybe_result =
-      isolate->heap()->AllocateFunctionContext(length, function);
-  if (!maybe_result->To(&result)) return maybe_result;
-
-  isolate->set_context(result);
-
-  return result;  // non-failure
+  return isolate->heap()->AllocateFunctionContext(length, function);
 }