Unify the IsShortcutCandidate predicate.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 3325024fd81a8697cd82fb1c7c89279a79c7464c..7dfa142ad76d48cdce1a4b9252bfea7ed6eb3a98 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -619,16 +619,21 @@ const uint32_t kShortExternalStringTag = 0x10;
 
 
 // A ConsString with an empty string as the right side is a candidate
-// for being shortcut by the garbage collector unless it is internalized.
-// It's not common to have non-flat internalized strings, so we do not
-// shortcut them thereby avoiding turning internalized strings into strings.
-// See heap.cc and mark-compact.cc.
+// for being shortcut by the garbage collector. We don't allocate any
+// non-flat internalized strings, so we do not shortcut them thereby
+// avoiding turning internalized strings into strings. The bit-masks
+// below contain the internalized bit as additional safety.
+// See heap.cc, mark-compact.cc and objects-visiting.cc.
 const uint32_t kShortcutTypeMask =
     kIsNotStringMask |
     kIsNotInternalizedMask |
     kStringRepresentationMask;
 const uint32_t kShortcutTypeTag = kConsStringTag | kNotInternalizedTag;
 
+static inline bool IsShortcutCandidate(int type) {
+  return ((type & kShortcutTypeMask) == kShortcutTypeTag);
+}
+
 
 enum InstanceType {
   // String types.