Don't internalize names that are array indexes since they aren't used for lookup (the index is)

This should restore the splay regression.

BUG=

Review URL: https://codereview.chromium.org/1714753003

Cr-Commit-Position: refs/heads/master@{#34144}

src/factory.cc

@@ -2229,9 +2229,6 @@ Handle<String> Factory::NumberToString(Handle<Object> number,
   // We tenure the allocated string since it is referenced from the
   // number-string cache which lives in the old space.
   Handle<String> js_string = NewStringFromAsciiChecked(str, TENURED);
-  // Make sure the string cached in the number cache is also the internalized
-  // version of the same string.
-  js_string = InternalizeString(js_string);
   SetNumberStringCache(number, js_string);
   return js_string;
 }

src/lookup.cc

@@ -38,7 +38,7 @@ LookupIterator LookupIterator::PropertyOrElement(Isolate* isolate,
     LookupIterator it(isolate, receiver, index, configuration);
     // Here we try to avoid having to rebuild the string later
     // by storing it on the indexed LookupIterator.
-    it.name_ = isolate->factory()->InternalizeName(name);
+    it.name_ = name;
     return it;
   }
 

src/lookup.h

@@ -127,27 +127,27 @@ class LookupIterator final BASE_EMBEDDED {
   static LookupIterator PropertyOrElement(
       Isolate* isolate, Handle<Object> receiver, Handle<Name> name,
       Configuration configuration = DEFAULT) {
-    name = isolate->factory()->InternalizeName(name);
     uint32_t index;
-    LookupIterator it =
-        name->AsArrayIndex(&index)
-            ? LookupIterator(isolate, receiver, index, configuration)
-            : LookupIterator(receiver, name, configuration);
-    it.name_ = name;
-    return it;
+    if (name->AsArrayIndex(&index)) {
+      LookupIterator it =
+          LookupIterator(isolate, receiver, index, configuration);
+      it.name_ = name;
+      return it;
+    }
+    return LookupIterator(receiver, name, configuration);
   }
 
   static LookupIterator PropertyOrElement(
       Isolate* isolate, Handle<Object> receiver, Handle<Name> name,
       Handle<JSReceiver> holder, Configuration configuration = DEFAULT) {
-    name = isolate->factory()->InternalizeName(name);
     uint32_t index;
-    LookupIterator it =
-        name->AsArrayIndex(&index)
-            ? LookupIterator(isolate, receiver, index, holder, configuration)
-            : LookupIterator(receiver, name, holder, configuration);
-    it.name_ = name;
-    return it;
+    if (name->AsArrayIndex(&index)) {
+      LookupIterator it =
+          LookupIterator(isolate, receiver, index, holder, configuration);
+      it.name_ = name;
+      return it;
+    }
+    return LookupIterator(receiver, name, holder, configuration);
   }
 
   static LookupIterator PropertyOrElement(