Fixed pointer arithmetic in write barrier for large objects when marking progress bar is used.

BUG=

Review URL: https://codereview.chromium.org/11421123

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13073 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/spaces.h

@@ -506,7 +506,7 @@ class MemoryChunk {
   bool IsLeftOfProgressBar(Object** slot) {
     Address slot_address = reinterpret_cast<Address>(slot);
     ASSERT(slot_address > this->address());
-    return (slot_address - this->address() + kObjectStartOffset) <
+    return (slot_address - (this->address() + kObjectStartOffset)) <
            progress_bar();
   }