More cleanly separate adding from setting elements

This is a first step towards disentangling the backend code. In the future we should just use ElementsAccessors.
BUG=v8:4137
LOG=n

Review URL: https://codereview.chromium.org/1177043012

Cr-Commit-Position: refs/heads/master@{#29111}

src/lookup.cc

@@ -173,21 +173,17 @@ void LookupIterator::ReconfigureDataProperty(Handle<Object> value,
   Handle<JSObject> holder = GetHolder<JSObject>();
   if (IsElement()) {
     // TODO(verwaest): Clean up.
-    if (attributes == NONE && !holder->HasDictionaryElements() &&
-        !holder->HasDictionaryArgumentsElements()) {
-      ElementsAccessor* accessor = holder->GetElementsAccessor();
-      accessor->Set(holder, index(), value);
+    DCHECK(holder->HasFastElements() || holder->HasDictionaryElements() ||
+           holder->HasSloppyArgumentsElements());
+    DCHECK(attributes != NONE || !holder->HasFastElements());
+    Handle<SeededNumberDictionary> d = JSObject::NormalizeElements(holder);
+    // TODO(verwaest): Move this into NormalizeElements.
+    d->set_requires_slow_elements();
+    if (holder->HasDictionaryElements()) {
+      JSObject::SetDictionaryElement(holder, index(), value, attributes);
     } else {
-      DCHECK(holder->HasFastElements() || holder->HasDictionaryElements() ||
-             holder->HasSloppyArgumentsElements());
-      Handle<SeededNumberDictionary> d = JSObject::NormalizeElements(holder);
-      // TODO(verwaest): Move this into NormalizeElements.
-      d->set_requires_slow_elements();
-      if (holder->HasDictionaryElements()) {
-        JSObject::SetDictionaryElement(holder, index(), value, attributes);
-      } else {
-        JSObject::SetSloppyArgumentsElement(holder, index(), value, attributes);
-      }
+      JSObject::SetDictionaryArgumentsElement(holder, index(), value,
+                                              attributes);
     }
   } else if (holder_map_->is_dictionary_map()) {
     PropertyDetails details(attributes, v8::internal::DATA, 0,

src/objects.h

@@ -1899,16 +1899,23 @@ class JSObject: public JSReceiver {
   static void SetNormalizedProperty(Handle<JSObject> object, Handle<Name> name,
                                     Handle<Object> value,
                                     PropertyDetails details);
-  static void SetDictionaryElement(Handle<JSObject> object, uint32_t index,
+  static void AddDictionaryElement(Handle<JSObject> object, uint32_t index,
                                    Handle<Object> value,
                                    PropertyAttributes attributes);
-  static void SetSloppyArgumentsElement(Handle<JSObject> object, uint32_t index,
+  static void AddSloppyArgumentsElement(Handle<JSObject> object, uint32_t index,
                                         Handle<Object> value,
                                         PropertyAttributes attributes);
+  static void SetDictionaryElement(Handle<JSObject> object, uint32_t index,
+                                   Handle<Object> value,
+                                   PropertyAttributes attributes);
+  static void SetDictionaryArgumentsElement(Handle<JSObject> object,
+                                            uint32_t index,
+                                            Handle<Object> value,
+                                            PropertyAttributes attributes);
 
-  static void SetFastElement(Handle<JSObject> object, uint32_t index,
+  static void AddFastElement(Handle<JSObject> object, uint32_t index,
                              Handle<Object> value);
-  static void SetFastDoubleElement(Handle<JSObject> object, uint32_t index,
+  static void AddFastDoubleElement(Handle<JSObject> object, uint32_t index,
                                    Handle<Object> value);
 
   static void OptimizeAsPrototype(Handle<JSObject> object,