KeyedStoreIC must immediately make prototypes fast

as opposed to waiting until state() is PREMONOMORPHIC like named
Load/StoreICs do. Keyed ICs do not have PREMONOMORPHIC state.

Bug: v8:6999
Change-Id: If37705d3301fb93a2fc2bf10fdeb255ff06fdb5e
Reviewed-on: https://chromium-review.googlesource.com/737655
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48895}

src/ic/ic.cc

@@ -1873,9 +1873,7 @@ MaybeHandle<Object> KeyedStoreIC::Store(Handle<Object> object,
     return store_handle;
   }
 
-  if (state() != UNINITIALIZED) {
-    JSObject::MakePrototypesFast(object, kStartAtPrototype, isolate());
-  }
+  JSObject::MakePrototypesFast(object, kStartAtPrototype, isolate());
 
   bool use_ic = FLAG_use_ic && !object->IsStringWrapper() &&
                 !object->IsAccessCheckNeeded() && !object->IsJSGlobalProxy();