[Media>UI] Apply throttling if the notification is updated too frequently

chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java

Index: chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java b/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java
index 815761f11efc5f6a21b487996a14f94597b8335c..40b60ab945e5666bb4b24ce5f2ebd74dc7449e50 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java
@@ -21,7 +21,9 @@ import android.graphics.drawable.BitmapDrawable;
 import android.graphics.drawable.Drawable;
 import android.media.AudioManager;
 import android.os.Build;
+import android.os.Handler;
 import android.os.IBinder;
+import android.support.annotation.NonNull;
 import android.support.v4.app.NotificationManagerCompat;
 import android.support.v4.media.MediaMetadataCompat;
 import android.support.v4.media.session.MediaSessionCompat;
@@ -33,6 +35,7 @@ import android.util.SparseArray;
 import android.view.KeyEvent;
 
 import org.chromium.base.ContextUtils;
+import org.chromium.base.Log;
 import org.chromium.base.SysUtils;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.blink.mojom.MediaSessionAction;
@@ -129,6 +132,98 @@ public class MediaNotificationManager {
     @VisibleForTesting
     MediaSessionCompat mMediaSession;
 
+    @VisibleForTesting
+    Throttler mThrottler;
+
+    @VisibleForTesting
+    static class Throttler {
+        @VisibleForTesting
+        static final int THROTTLE_MILLIS = 500;
+
+        @VisibleForTesting
+        MediaNotificationManager mManager;
+
+        private final Handler mHandler;
+
+        @VisibleForTesting
+        Throttler(@NonNull MediaNotificationManager manager) {
+            mManager = manager;
+            mHandler = new Handler();
+        }
+
+        // When |mTask| is non-null, it will always be queued in mHandler. When |mTask| is non-null,
+        // all notification updates will be throttled and their info will be stored as
+        // mLastPendingInfo. When |mTask| fires, it will call {@link showNotification()} with
+        // the latest queued notification info.
+        @VisibleForTesting
+        Runnable mTask;
+
+        // The last pending info. If non-null, it will be the latest notification info.
+        // Otherwise, the latest notification info will be |mManager.mMediaNotificationInfo|.
+        @VisibleForTesting
+        MediaNotificationInfo mLastPendingInfo;
+
+        /**
+         * Queue |mediaNotificationInfo| for update. In unthrottled state (i.e. |mTask| != null),
+         * the notification will be updated immediately and enter the throttled state. In
+         * unthrottled state, the method will only update the pending notification info, which will
+         * be used for updating the notification when |mTask| is fired.
+         *
+         * @param mediaNotificationInfo The notification info to be queued.
+         */
+        public void queueNotification(MediaNotificationInfo mediaNotificationInfo) {
+            assert mediaNotificationInfo != null;
+
+            MediaNotificationInfo latestMediaNotificationInfo =
+                    mLastPendingInfo != null ? mLastPendingInfo : mManager.mMediaNotificationInfo;
+
+            if (shouldIgnoreMediaNotificationInfo(
+                        latestMediaNotificationInfo, mediaNotificationInfo)) {
+                return;
+            }
+
+            if (mTask == null) {
+                showNotificationImmediately(mediaNotificationInfo);
+            } else {
+                mLastPendingInfo = mediaNotificationInfo;
+            }
+        }
+
+        /**
+         * Clears the pending notification and enter unthrottled state.
+         */
+        public void clearPendingNotifications() {
+            mHandler.removeCallbacks(mTask);
+            mLastPendingInfo = null;
+            mTask = null;
+        }
+
+        @VisibleForTesting
+        void showNotificationImmediately(MediaNotificationInfo mediaNotificationInfo) {
+            // If no notification hasn't been updated in the last THROTTLE_MILLIS, update
+            // immediately and queue a task for blocking further updates.
+            mManager.showNotification(mediaNotificationInfo);
+            mTask = new Runnable() {
+                @Override
+                public void run() {
+                    if (mLastPendingInfo != null) {
+                        // If any notification info is pended during the throttling time window,
+                        // update the notification.
+                        showNotificationImmediately(mLastPendingInfo);
+                        mLastPendingInfo = null;
+                    } else {
+                        // Otherwise, clear the task so further update is unthrottled.
+                        mTask = null;
+                    }
+                }
+            };
+            if (!mHandler.postDelayed(mTask, THROTTLE_MILLIS)) {
+                Log.w(TAG, "Failed to post the throttler task.");
+                mTask = null;
+            }
+        }
+    }
+
     private final MediaSessionCompat.Callback mMediaSessionCallback =
             new MediaSessionCompat.Callback() {
                 @Override
@@ -468,7 +563,7 @@ public class MediaNotificationManager {
             sManagers.put(notificationInfo.id, manager);
         }
 
-        manager.showNotification(notificationInfo);
+        manager.mThrottler.queueNotification(notificationInfo);
     }
 
     /**
@@ -644,6 +739,8 @@ public class MediaNotificationManager {
                 new MediaButtonInfo(R.drawable.ic_fast_rewind_white_36dp,
                         R.string.accessibility_seek_backward,
                         ListenerService.ACTION_SEEK_BACKWARD));
+
+        mThrottler = new Throttler(this);
     }
 
     /**
@@ -692,9 +789,7 @@ public class MediaNotificationManager {
 
     @VisibleForTesting
     void showNotification(MediaNotificationInfo mediaNotificationInfo) {
-        if (mediaNotificationInfo.equals(mMediaNotificationInfo)) return;
-        if (mediaNotificationInfo.isPaused && mMediaNotificationInfo != null
-                && mediaNotificationInfo.tabId != mMediaNotificationInfo.tabId) {
+        if (shouldIgnoreMediaNotificationInfo(mMediaNotificationInfo, mediaNotificationInfo)) {
             return;
         }
 
@@ -715,7 +810,15 @@ public class MediaNotificationManager {
         }
     }
 
-    private void clearNotification() {
+    private static boolean shouldIgnoreMediaNotificationInfo(
+            MediaNotificationInfo oldInfo, MediaNotificationInfo newInfo) {
+        return newInfo.equals(oldInfo)
+                || ((newInfo.isPaused && oldInfo != null && newInfo.tabId != oldInfo.tabId));
+    }
+
+    @VisibleForTesting
+    void clearNotification() {
+        mThrottler.clearPendingNotifications();
         if (mMediaNotificationInfo == null) return;
 
         NotificationManagerCompat manager = NotificationManagerCompat.from(getContext());