Make maps in monomorphic IC stubs weak.

src/handles.cc

Index: src/handles.cc
diff --git a/src/handles.cc b/src/handles.cc
index edb657c53dc95bf61544acb3275266480d55976c..09ba7a0ceea673161fbe6d3b79269cfacd22b22b 100644
--- a/src/handles.cc
+++ b/src/handles.cc
@@ -763,7 +763,7 @@ void AddWeakObjectToCodeDependency(Heap* heap,
                                    Handle<Code> code) {
   heap->EnsureWeakObjectToCodeTable();
   Handle<DependentCode> dep(heap->LookupWeakObjectToCodeDependency(*object));
-  dep = DependentCode::Insert(dep, DependentCode::kWeaklyEmbeddedGroup, code);
+  dep = DependentCode::Insert(dep, DependentCode::kWeakCodeGroup, code);
   CALL_HEAP_FUNCTION_VOID(heap->isolate(),
                           heap->AddWeakObjectToCodeDependency(*object, *dep));
 }