Fix SingleCategoryPreference crash for chosen objs

This change fixes a crash that occurs when trying to view the USB
preferences when a device has been granted permission to a site. The
crash is caused because addChosenObjects() does not check if |mSearch|
is null first before checking if the String is empty.

Bug: 923593
Change-Id: I772e4357361653e7b5e0ce41691e7832d525a68a
Reviewed-on: https://chromium-review.googlesource.com/c/1427740Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Ovidio de Jesús Ruiz-Henríquez <odejesush@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626185}

chrome/android/java/src/org/chromium/chrome/browser/preferences/website/SingleCategoryPreferences.java

@@ -706,7 +706,8 @@ public class SingleCategoryPreferences extends PreferenceFragment
         // that have permission to access each.
         for (Website site : sites) {
             for (ChosenObjectInfo info : site.getChosenObjectInfo()) {
-                if (mSearch.isEmpty() || info.getName().toLowerCase().contains(mSearch)) {
+                if (mSearch == null || mSearch.isEmpty()
+                        || info.getName().toLowerCase().contains(mSearch)) {
                     Pair<ArrayList<ChosenObjectInfo>, ArrayList<Website>> entry =
                             objects.get(info.getObject());
                     if (entry == null) {