Make maps in monomorphic IC stubs weak.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index e8e20e9a3fe9bf0374bfd07a58562b73a31cb9ab..a42c0a8e75b80c3acc4f69ee2acca4f91bf2047b 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -5314,6 +5314,12 @@ class Code: public HeapObject {
   inline bool is_to_boolean_ic_stub() { return kind() == TO_BOOLEAN_IC; }
   inline bool is_keyed_stub();
   inline bool is_optimized_code() { return kind() == OPTIMIZED_FUNCTION; }
+  inline bool is_weak_stub() {
+    Kind k = kind();
+    return (k == LOAD_IC || k == STORE_IC || k == KEYED_LOAD_IC ||
+            k == KEYED_STORE_IC || k == COMPARE_NIL_IC) &&
+           ic_state() == MONOMORPHIC;
+  }
 
   inline void set_raw_kind_specific_flags1(int value);
   inline void set_raw_kind_specific_flags2(int value);
@@ -5571,11 +5577,17 @@ class Code: public HeapObject {
   void VerifyEmbeddedObjectsDependency();
 #endif
 
+  inline bool CanContainWeakObjects() {
+    return is_optimized_code() || is_weak_stub();
+  }
+
   inline bool IsWeakObject(Object* object) {
-    return is_optimized_code() && IsWeakObjectInOptimizedCode(object);
+    return (is_optimized_code() && IsWeakObjectInOptimizedCode(object)) ||
+           (is_weak_stub() && IsWeakObjectInIC(object));
   }
 
   inline bool IsWeakObjectInOptimizedCode(Object* object);
+  inline bool IsWeakObjectInIC(Object* object);
 
   // Max loop nesting marker used to postpose OSR. We don't take loop
   // nesting that is deeper than 5 levels into account.