Properly pass InitializationFlag back from ScriptContextTable lookups

This was dropped accidentally in bb97d27a.

R=verwaest@chromium.org
BUG=chromium:633884

Review-Url: https://codereview.chromium.org/2203213003
Cr-Commit-Position: refs/heads/master@{#38345}

src/contexts.cc

@@ -233,6 +233,7 @@ Handle<Object> Context::Lookup(Handle<String> name, ContextLookupFlags flags,
           }
           *index = r.slot_index;
           *variable_mode = r.mode;
+          *init_flag = r.init_flag;
           *attributes = GetAttributesForMode(r.mode);
           return ScriptContextTable::GetContext(script_contexts,
                                                 r.context_index);

test/mjsunit/regress/regress-crbug-633884.js

+// Copyright 2016 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.
+
+try {
+  // Leave "blarg" as the hole in a new ScriptContext.
+  Realm.eval(Realm.current(), "throw Error(); let blarg");
+} catch (e) { }
+
+// Access "blarg" via a dynamic lookup. Should not crash!
+assertThrows(function() {
+  // Prevent full-codegen from optimizing away the %LoadLookupSlot call.
+  eval("var x = 5");
+  blarg;
+});