Monomorphic prototype failures should be reserved for already-seen keys.

src/ic.h

Index: src/ic.h
diff --git a/src/ic.h b/src/ic.h
index e70cb82c96d59e132ce3994d5f099fc0c183cdad..146b26b28306b8192b3092615c40e2169d2156c8 100644
--- a/src/ic.h
+++ b/src/ic.h
@@ -96,8 +96,14 @@ class IC {
 
   // Compute the current IC state based on the target stub, receiver and name.
   void UpdateState(Handle<Object> receiver, Handle<Object> name);
-  void MarkMonomorphicPrototypeFailure() {
-    state_ = MONOMORPHIC_PROTOTYPE_FAILURE;
+
+  bool IsNameCompatibleWithMonomorphicPrototypeFailure(Handle<Object> name);
+  bool TryMarkMonomorphicPrototypeFailure(Handle<Object> name) {
+    if (IsNameCompatibleWithMonomorphicPrototypeFailure(name)) {
+      state_ = MONOMORPHIC_PROTOTYPE_FAILURE;
+      return true;
+    }
+    return false;
   }
 
   // Clear the inline cache to initial state.