Make maps in monomorphic IC stubs weak.

src/ic.h

Index: src/ic.h
diff --git a/src/ic.h b/src/ic.h
index 41882e66890809936332c66762d85094bd4756c4..ca0398897cdca74eeff9f6bafe31df824291e330 100644
--- a/src/ic.h
+++ b/src/ic.h
@@ -106,6 +106,14 @@ class IC {
     return false;
   }
 
+  // If the stub contains weak maps then this function adds the stub to
+  // the dependent code array of each weak map.
+  static void RegisterWeakMapDependency(Handle<Code> stub);
+
+  // This function is called when a weak map in the stub is dying,
+  // invalidates the stub by setting maps in it to undefined.
+  static void InvalidateMaps(Code* stub);
+
   // Clear the inline cache to initial state.
   static void Clear(Isolate* isolate,
                     Address address,
@@ -173,6 +181,9 @@ class IC {
 
   // Set the call-site target.
   void set_target(Code* code) {
+#ifdef VERIFY_HEAP
+    code->VerifyEmbeddedObjectsDependency();
+#endif
     SetTargetAtAddress(address(), code, constant_pool());
     target_set_ = true;
   }