Add sanity check to CodeFlusher::AddCandidate.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index 8821c3df30a3b00d3b9139410b7022547604fbd4..b34be6b91daabf696440b607e23a8c7532859130 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -423,6 +423,10 @@ class CodeFlusher {
     if (GetNextCandidate(shared_info) == NULL) {
       SetNextCandidate(shared_info, shared_function_info_candidates_head_);
       shared_function_info_candidates_head_ = shared_info;
+    } else {
+      // TODO(mstarzinger): Active in release mode to flush out problems.
+      // Should be turned back into an ASSERT or removed completely.
+      CHECK(ContainsCandidate(shared_info));
     }
   }
 
@@ -434,6 +438,8 @@ class CodeFlusher {
     }
   }
 
+  bool ContainsCandidate(SharedFunctionInfo* shared_info);
+
   void EvictCandidate(SharedFunctionInfo* shared_info);
   void EvictCandidate(JSFunction* function);