Add sanity check to CodeFlusher::AddCandidate.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 2c6d9d1c93687b96bfa4144638374982289c199d..9cfe5e04821ae38592dfa77edcc03e48fe787b69 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -933,6 +933,16 @@ void CodeFlusher::ProcessSharedFunctionInfoCandidates() {
 }
 
 
+bool CodeFlusher::ContainsCandidate(SharedFunctionInfo* shared_info) {
+  SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
+  while (candidate != NULL) {
+    if (candidate == shared_info) return true;
+    candidate = GetNextCandidate(candidate);
+  }
+  return false;
+}
+
+
 void CodeFlusher::EvictCandidate(SharedFunctionInfo* shared_info) {
   // The function is no longer a candidate, make sure it gets visited
   // again so that previous flushing decisions are revisited.