[cleanup] Add Elements() to ArrayList.

ArrayList is a FixedArray where kFirstIndex is > 0. The
Elements() methods returns a copy of the elements starting at
kFirstIndex, i.e., without the length that is stored in the first
slot.

Drive-by fix: Rename some variables.

BUG=

Change-Id: Ia1de73c4780a179301007f2ab9080fd08e8ea99d
Reviewed-on: https://chromium-review.googlesource.com/466186Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Franziska Hinkelmann <franzih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44365}

src/feedback-vector.cc

@@ -926,19 +926,19 @@ void CollectTypeProfileNexus::Collect(Handle<String> type, int position) {
         UnseededNumberDictionary::cast(feedback), isolate);
   }
 
-  Handle<ArrayList> types_for_position;
+  Handle<ArrayList> position_specific_types;
 
   if (types->Has(position)) {
     int entry = types->FindEntry(position);
     DCHECK(types->ValueAt(entry)->IsArrayList());
-    types_for_position =
+    position_specific_types =
         Handle<ArrayList>(ArrayList::cast(types->ValueAt(entry)));
   } else {
-    types_for_position = ArrayList::New(isolate, 1);
+    position_specific_types = ArrayList::New(isolate, 1);
   }
 
   types = UnseededNumberDictionary::Set(
-      types, position, ArrayList::Add(types_for_position, type));
+      types, position, ArrayList::Add(position_specific_types, type));
   SetFeedback(*types);
 }
 
@@ -957,19 +957,14 @@ Handle<JSObject> ConvertToJSObject(Isolate* isolate,
     if (key->IsSmi()) {
       int value_index = index + UnseededNumberDictionary::kEntryValueIndex;
 
-      Handle<ArrayList> orig = Handle<ArrayList>(
+      Handle<ArrayList> position_specific_types = Handle<ArrayList>(
           ArrayList::cast(feedback->get(value_index)), isolate);
 
-      // Delete the first entry, i.e., the length.
-      Handle<FixedArray> storage =
-          isolate->factory()->NewFixedArray(orig->Length());
-      orig->CopyTo(1, *storage, 0, orig->Length());
-
-      int pos = Smi::cast(key)->value();
-      JSObject::AddDataElement(
-          type_profile, pos,
-          isolate->factory()->NewJSArrayWithElements(storage),
-          PropertyAttributes::NONE)
+      int position = Smi::cast(key)->value();
+      JSObject::AddDataElement(type_profile, position,
+                               isolate->factory()->NewJSArrayWithElements(
+                                   position_specific_types->Elements()),
+                               PropertyAttributes::NONE)
           .ToHandleChecked();
     }
   }

src/objects.cc

@@ -10039,6 +10039,13 @@ Handle<ArrayList> ArrayList::New(Isolate* isolate, int size) {
   return result;
 }
 
+Handle<FixedArray> ArrayList::Elements() {
+  Handle<FixedArray> result = GetIsolate()->factory()->NewFixedArray(Length());
+  // Do not copy the first entry, i.e., the length.
+  CopyTo(kFirstIndex, *result, 0, Length());
+  return result;
+}
+
 bool ArrayList::IsFull() {
   int capacity = length();
   return kFirstIndex + Length() == capacity;

src/objects.h

@@ -2966,6 +2966,9 @@ class ArrayList : public FixedArray {
   inline void Set(int index, Object* obj,
                   WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
   inline void Clear(int index, Object* undefined);
+
+  // Return a copy of the list without the first entry (contains the Length).
+  Handle<FixedArray> Elements();
   bool IsFull();
   DECLARE_CAST(ArrayList)