Let FastCloneShallowObjectStub work with empty literal objects.

src/code-stubs-hydrogen.cc

 // Copyright 2012 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/bailout-reason.h"
 #include "src/code-stubs.h"
 #include "src/field-index.h"
 #include "src/hydrogen.h"
@@ skipping 398 matching lines @@
   IfBuilder checker(this);
   checker.IfNot<HCompareObjectEqAndBranch, HValue*>(allocation_site,
                                                     undefined);
   checker.And();
 
   HObjectAccess access = HObjectAccess::ForAllocationSiteOffset(
       AllocationSite::kTransitionInfoOffset);
   HInstruction* boilerplate = Add<HLoadNamedField>(
       allocation_site, static_cast<HValue*>(NULL), access);
 
-  int size = JSObject::kHeaderSize + casted_stub()->length() * kPointerSize;
+  int length = casted_stub()->length();
+  if (length == 0) {
+    // Empty objects have some slack added to them.
+    length = JSObject::kInitialGlobalObjectUnusedPropertiesCount;
+  }
+  int size = JSObject::kHeaderSize + length * kPointerSize;
   int object_size = size;
   if (FLAG_allocation_site_pretenuring) {
     size += AllocationMemento::kSize;
   }
 
   HValue* boilerplate_map = Add<HLoadNamedField>(
       boilerplate, static_cast<HValue*>(NULL),
       HObjectAccess::ForMap());
   HValue* boilerplate_size = Add<HLoadNamedField>(
       boilerplate_map, static_cast<HValue*>(NULL),
@@ skipping 1584 matching lines @@
 
   // Probe the stub cache.
   Code::Flags flags = Code::RemoveTypeAndHolderFromFlags(
       Code::ComputeHandlerFlags(Code::LOAD_IC));
   Add<HTailCallThroughMegamorphicCache>(receiver, name, flags);
 
   // We never continue.
   return graph()->GetConstant0();
 }
 } }  // namespace v8::internal