Introduce {FAST,SLOW}_STRING_WRAPPER_ELEMENTS

src/ic/ic-compiler.cc

Index: src/ic/ic-compiler.cc
diff --git a/src/ic/ic-compiler.cc b/src/ic/ic-compiler.cc
index ae4b2a5d58c9ab80e4793adee894de68a8659624..281557edd8a5b53a5216a6ac9b91207eaac9e9fa 100644
--- a/src/ic/ic-compiler.cc
+++ b/src/ic/ic-compiler.cc
@@ -49,7 +49,6 @@ Handle<Code> PropertyICCompiler::ComputeKeyedLoadMonomorphicHandler(
   if (receiver_map->has_indexed_interceptor()) {
     stub = LoadIndexedInterceptorStub(isolate).GetCode();
   } else if (receiver_map->IsStringMap()) {
-    // We have a string.
     stub = LoadIndexedStringStub(isolate).GetCode();
   } else if (receiver_map->has_sloppy_arguments_elements()) {
     stub = KeyedLoadSloppyArgumentsStub(isolate).GetCode();
@@ -58,6 +57,7 @@ Handle<Code> PropertyICCompiler::ComputeKeyedLoadMonomorphicHandler(
     stub = LoadFastElementStub(isolate, is_js_array, elements_kind,
                                convert_hole_to_undefined).GetCode();
   } else {
+    DCHECK(receiver_map->has_dictionary_elements());
     stub = LoadDictionaryElementStub(isolate, LoadICState(extra_ic_state))
                .GetCode();
   }