Adding a nullcheck into WinowAndroid.setPreferredRefreshRate.

We are getting a crash in org.chromium.ui.base.WindowAndroid.setPreferredRefreshRate because getWindow() returns null and there is no nullcheck there. getWindow() CAN return null when there is no activity (and this is exactly our case, Oculus Browser is not using Activity). There are getWindow() nullchecks in other methods of WindowAndroid, but not in setPreferredRefreshRate which looks as oversight.

Bug: 1085160
Change-Id: I6cbeac08787f9664abd4fdb2e619e100a09fa943
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2210673Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770793}

ui/android/java/src/org/chromium/ui/base/WindowAndroid.java

@@ -946,6 +946,7 @@ public class WindowAndroid implements AndroidPermissionDelegate, DisplayAndroidO
 
         int preferredModeId = getPreferredModeId(preferredRefreshRate);
         Window window = getWindow();
+        if (window == null) return;
         WindowManager.LayoutParams params = window.getAttributes();
         if (params.preferredDisplayModeId == preferredModeId) return;