harmony-scoping: Implement LoadIC handler for loads from global contexts.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 6184bb9e46b25c6a22015b216a3e60046a537f2d..e3bbac50e0ccd6cc789711f353d81be305769d92 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -5376,6 +5376,20 @@ void HOptimizedGraphBuilder::VisitVariableProxy(VariableProxy* expr) {
       }
 
       Handle<GlobalObject> global(current_info()->global_object());
+
+      Handle<GlobalContextTable> global_contexts(
+          global->native_context()->global_context_table());
+      GlobalContextTable::LookupResult lookup;
+      if (GlobalContextTable::Lookup(global_contexts, variable->name(),
+                                     &lookup)) {
+        Handle<Context> global_context = GlobalContextTable::GetContext(
+            global_contexts, lookup.context_index);
+        HInstruction* result = New<HLoadNamedField>(
+            Add<HConstant>(global_context), static_cast<HValue*>(NULL),
+            HObjectAccess::ForContextSlot(lookup.slot_index));
+        return ast_context()->ReturnInstruction(result, expr->id());
+      }
+
       LookupIterator it(global, variable->name(),
                         LookupIterator::OWN_SKIP_INTERCEPTOR);
       GlobalPropertyAccess type = LookupGlobalProperty(variable, &it, LOAD);