ui/android: Missed adding observer in previous change.

R=ericrk@chromium.org

Bug: 937031
Change-Id: I0413728e3b18a6e807050137ec2428b52efe644a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1525451
Auto-Submit: Khushal <khushalsagar@chromium.org>
Reviewed-by: Eric Karl <ericrk@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641708}

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

@@ -239,6 +239,7 @@ public class WindowAndroid implements AndroidPermissionDelegate, DisplayAndroidO
         mOutstandingIntents = new SparseArray<>();
         mIntentErrors = new HashMap<>();
         mDisplayAndroid = display;
+        mDisplayAndroid.addObserver(this);
         // Temporary solution for flaky tests, see https://crbug.com/767624 for context
         try (StrictModeContext unused = StrictModeContext.allowDiskReads()) {
             mVSyncMonitor =