Put new global var semantics behind a flag until WebKit tests are cleaned up.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index d8da56ced5a4bc7c9f6e9b2f23226f3f5e1bc155..f3b6e2c6a7f9f585b77b44d63f6314fdd0f0c542 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -1300,7 +1300,10 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_DeclareGlobals) {
       // value of the variable if the property is already there.
       // Do the lookup locally only, see ES5 errata.
       LookupResult lookup(isolate);
-      global->LocalLookup(*name, &lookup);
+      if (FLAG_es52_globals)
+        global->LocalLookup(*name, &lookup);
+      else
+        global->Lookup(*name, &lookup);
       if (lookup.IsProperty()) {
         // We found an existing property. Unless it was an interceptor
         // that claims the property is absent, skip this declaration.