arc: Prevent NOTREACHED from arc_app_list_prefs in logs.

Some user feedbacks are overflown this message. This happens after
adding "arc.apps.default" prefs. "default" appeared in arc.apps listing.
Fix to check if this is valid crx id as it done in different places of
this file.

TEST=Manually
BUG=b/117566030

Change-Id: I79384e58ab31593f571b2ce4542dfbfbc3d2447f
Reviewed-on: https://chromium-review.googlesource.com/c/1289992Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yury Khmel <khmel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600962}

chrome/browser/ui/app_list/arc/arc_app_list_prefs.cc

@@ -1389,6 +1389,9 @@ std::unordered_set<std::string> ArcAppListPrefs::GetAppsAndShortcutsForPackage(
       prefs_->GetDictionary(arc::prefs::kArcApps);
   for (base::DictionaryValue::Iterator app_it(*apps); !app_it.IsAtEnd();
        app_it.Advance()) {
+    if (!crx_file::id_util::IdIsValid(app_it.key()))
+      continue;
+
     const base::Value* value = &app_it.value();
     const base::DictionaryValue* app;
     if (!value->GetAsDictionary(&app)) {
@@ -1398,7 +1401,7 @@ std::unordered_set<std::string> ArcAppListPrefs::GetAppsAndShortcutsForPackage(
 
     std::string app_package;
     if (!app->GetString(kPackageName, &app_package)) {
-      NOTREACHED();
+      LOG(ERROR) << "App is malformed: " << app_it.key();
       continue;
     }