[stubs] Use a single slot for context globals.

src/contexts.cc

 // Copyright 2011 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.
 
 #include "src/v8.h"
 
 #include "src/bootstrapper.h"
 #include "src/debug.h"
 #include "src/scopeinfo.h"
 
@@ skipping 347 matching lines @@
 
   ScopeInfo* scope_info = ScopeInfo::cast(extension());
 
   int context_globals = scope_info->ContextGlobalCount();
   if (context_globals > 0) {
     PropertyCell* empty_cell = GetHeap()->empty_property_cell();
 
     int context_locals = scope_info->ContextLocalCount();
     int index = Context::MIN_CONTEXT_SLOTS + context_locals;
     for (int i = 0; i < context_globals; i++) {
-      // Clear both read and write slots.
-      set(index++, empty_cell);
       set(index++, empty_cell);
     }
   }
 }
 
 
 void Context::AddOptimizedFunction(JSFunction* function) {
   DCHECK(IsNativeContext());
 #ifdef ENABLE_SLOW_DCHECKS
   if (FLAG_enable_slow_asserts) {
@@ skipping 130 matching lines @@
   // During bootstrapping we allow all objects to pass as global
   // objects. This is necessary to fix circular dependencies.
   return isolate->heap()->gc_state() != Heap::NOT_IN_GC ||
       isolate->bootstrapper()->IsActive() ||
       object->IsGlobalObject();
 }
 #endif
 
 }  // namespace internal
 }  // namespace v8