[turbofan] Tweak AllocationSite::CanTrack for TurboFan.

This adapts the predicate in question to be geared towards TurboFan now
that Crankshaft is no longer being used. It makes the predicate respect
the --allocation-site-pretenuring flag again in all cases.

R=mlippautz@chromium.org
BUG=v8:6408

Change-Id: Ib2753f70d7904764859a2d91815a675745416239
Reviewed-on: https://chromium-review.googlesource.com/541321Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46058}

src/objects-inl.h

@@ -1175,16 +1175,11 @@ bool AllocationSite::ShouldTrack(ElementsKind boilerplate_elements_kind) {
 }
 
 inline bool AllocationSite::CanTrack(InstanceType type) {
-  if (FLAG_turbo) {
+  if (FLAG_allocation_site_pretenuring) {
     // TurboFan doesn't care at all about String pretenuring feedback,
     // so don't bother even trying to track that.
     return type == JS_ARRAY_TYPE || type == JS_OBJECT_TYPE;
   }
-  if (FLAG_allocation_site_pretenuring) {
-    return type == JS_ARRAY_TYPE ||
-        type == JS_OBJECT_TYPE ||
-        type < FIRST_NONSTRING_TYPE;
-  }
   return type == JS_ARRAY_TYPE;
 }