Distinguish weak references in heap snapshots, group GC roots.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 60af1eee8a31de314c4be560f06870b97ffd3da5..fa038f512efdacc40984375e9fc6e72768ca170f 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -7639,6 +7639,22 @@ void SharedFunctionInfo::CompleteInobjectSlackTracking() {
 }
 
 
+#define DECLARE_TAG(ignore1, name, ignore2) name,
+const char* VisitorSynchronization::kTags[
+    VisitorSynchronization::kNumberOfSyncTags] = {
+  VISITOR_SYNCHRONIZATION_TAGS_LIST(DECLARE_TAG)
+};
+#undef DECLARE_TAG
+
+
+#define DECLARE_TAG(ignore1, ignore2, name) name,
+const char* VisitorSynchronization::kTagNames[
+    VisitorSynchronization::kNumberOfSyncTags] = {
+  VISITOR_SYNCHRONIZATION_TAGS_LIST(DECLARE_TAG)
+};
+#undef DECLARE_TAG
+
+
 void ObjectVisitor::VisitCodeTarget(RelocInfo* rinfo) {
   ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode()));
   Object* target = Code::GetCodeFromTargetAddress(rinfo->target_address());