Use static_cast instead of reinterpret_cast for downcasting

static_cast is better suited for downcasting since it can check that the
types are related.

/chrome/browser/ui/ash/launcher
This CL was uploaded by git cl split.

R=skuhne@chromium.org

Change-Id: I4e9943d6a465583be28cb3bf940ad65499ed33e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2434774
Auto-Submit: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Stefan Kuhne <skuhne@chromium.org>
Commit-Queue: Stefan Kuhne <skuhne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811310}

chrome/browser/ui/ash/launcher/chrome_launcher_controller_unittest.cc

@@ -575,7 +575,7 @@ class ChromeLauncherControllerTest
     sync_preferences::PrefServiceSyncable* pref_sync =
         profile()->GetTestingPrefService();
     sync_preferences::PrefModelAssociator* pref_sync_service =
-        reinterpret_cast<sync_preferences::PrefModelAssociator*>(
+        static_cast<sync_preferences::PrefModelAssociator*>(
             pref_sync->GetSyncableService(GetPreferencesModelType()));
     return pref_sync_service;
   }