Decoupling MarkDescriptorArray as much as possible from the ContentArray.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index d87b3a041391366abfb3d016c40a9bebd5f33ff3..5ad67c98b3c1453518f8b0cd7fc14ad7f5cbe6ac 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1939,6 +1939,12 @@ String* DescriptorArray::GetKey(int descriptor_number) {
 }
 
 
+Object** DescriptorArray::GetValueSlot(int descriptor_number) {
+  ASSERT(descriptor_number < number_of_descriptors());
+  return GetContentArray()->data_start() + ToValueIndex(descriptor_number);
+}
+
+
 Object* DescriptorArray::GetValue(int descriptor_number) {
   ASSERT(descriptor_number < number_of_descriptors());
   return GetContentArray()->get(ToValueIndex(descriptor_number));