Bug 1503978 - Force fullscreen after PiP only if media is playing; r=JanH

Otherwise the user should see and be able to interact with the whole page.

Refactored `PictureInPictureController` to check the media playing status for
only the current tab, the one the user has in front and for which we may allow
PiP because `GeckoMediaControlAgent.isMediaPlaying()` would give us false
positives in the case where the current Tab is in fullscreen but not playing
media, while at the same time a background Tab is playing media.

BrowserApp will only force fullscreen after returning from PiP if media
playback has ended, but will keep fullscreen for playing/paused media.

Differential Revision: https://phabricator.services.mozilla.com/D19750

--HG--
extra : moz-landing-system : lando

mobile/android/base/java/org/mozilla/gecko/BrowserApp.java

@@ -1083,11 +1083,14 @@ public class BrowserApp extends GeckoApp
                 // by checking if the activity received onStop() or not.
                 final boolean userReturnedToFullApp = !isApplicationInBackground();
 
-                // After returning from Picture-in-picture mode the video will still be playing
+                // After returning from Picture-in-picture mode the video can still be playing
                 // in fullscreen. But now we have the status bar showing.
-                // Call setFullscreen(..) to hide it and offer the same fullscreen video experience
-                // that the user had before entering in Picture-in-picture mode.
-                if (userReturnedToFullApp) {
+                // If media is still playing / is paused we need to call setFullscreen(..) to hide
+                // the status bar and offer the same fullscreen video experience that the user had
+                // before entering in Picture-in-picture mode.
+                final boolean shouldKeepVideoInFullscreen =
+                        mPipController.isMediaPlaying() || mPipController.isMediaPaused();
+                if (userReturnedToFullApp && shouldKeepVideoInFullscreen) {
                     ActivityUtils.setFullScreen(this, true);
                 } else {
                     // User closed the PIP mode.

mobile/android/base/java/org/mozilla/gecko/media/PictureInPictureController.java

@@ -18,6 +18,8 @@ import org.mozilla.gecko.AppConstants;
 import org.mozilla.gecko.BuildConfig;
 import org.mozilla.gecko.EventDispatcher;
 import org.mozilla.gecko.R;
+import org.mozilla.gecko.Tab;
+import org.mozilla.gecko.Tabs;
 import org.mozilla.gecko.util.ActivityUtils;
 import org.mozilla.gecko.util.BundleEventListener;
 import org.mozilla.gecko.util.EventCallback;
@@ -32,6 +34,12 @@ public class PictureInPictureController implements BundleEventListener {
 
     private final Activity pipActivity;
     private boolean isInPipMode;
+    private PlaybackState playbackState = PlaybackState.STOPPED;
+    private enum PlaybackState {
+        PLAYING,
+        PAUSED,
+        STOPPED
+    }
 
     public PictureInPictureController(Activity activity) {
         pipActivity = activity;
@@ -44,7 +52,7 @@ public class PictureInPictureController implements BundleEventListener {
      */
     public void tryEnteringPictureInPictureMode() throws IllegalStateException {
         if (shouldTryPipMode() &&
-                pipActivity.enterPictureInPictureMode(getPipParams(isMediaPlaying()))) {
+                pipActivity.enterPictureInPictureMode(getPipParams(isMediaPlayingForCurrentTab()))) {
             EventDispatcher.getInstance().registerUiThreadListener(this, "MediaControlService:MediaPlayingStatus");
             isInPipMode = true;
         }
@@ -61,6 +69,18 @@ public class PictureInPictureController implements BundleEventListener {
         return isInPipMode;
     }
 
+    public boolean isMediaPlaying() {
+        return playbackState == PlaybackState.PLAYING;
+    }
+
+    public boolean isMediaPaused() {
+        return playbackState == PlaybackState.PAUSED;
+    }
+
+    public boolean isMediaStopped() {
+        return playbackState == PlaybackState.STOPPED;
+    }
+
     private boolean shouldTryPipMode() {
         if (!AppConstants.Versions.feature26Plus) {
             logDebugMessage("Picture In Picture is only available on Oreo+");
@@ -93,7 +113,7 @@ public class PictureInPictureController implements BundleEventListener {
             return false;
         }
 
-        if (!isMediaPlaying()) {
+        if (!isMediaPlayingForCurrentTab()) {
             logDebugMessage("Will not enter Picture in Picture mode if no media is playing");
             return false;
         }
@@ -157,8 +177,10 @@ public class PictureInPictureController implements BundleEventListener {
         return new Intent(action, null, pipActivity, MediaControlService.class);
     }
 
-    private boolean isMediaPlaying() {
-        return GeckoMediaControlAgent.isMediaPlaying();
+    private boolean isMediaPlayingForCurrentTab() {
+        final Tab currentTab = Tabs.getInstance().getSelectedTab();
+
+        return currentTab != null && currentTab.isMediaPlaying();
     }
 
     /**
@@ -193,15 +215,27 @@ public class PictureInPictureController implements BundleEventListener {
             Log.w(LOGTAG, "Can't extract new media status");
             return;
         }
+
+        // Best hope scenario: we received this events for the current tab, for which we may allow PiP
+        // We check against `isMediaPlayingForCurrentTab()` to be sure.
         switch (newMediaStatus) {
             case "resumeMedia":
-                updatePictureInPictureActions(getPipParams(true));
+                if (isMediaPlayingForCurrentTab()) {
+                    updatePictureInPictureActions(getPipParams(true));
+                    playbackState = PlaybackState.PLAYING;
+                }
                 break;
             case "mediaControlPaused":
-                updatePictureInPictureActions(getPipParams(false));
+                if (!isMediaPlayingForCurrentTab()) {
+                    updatePictureInPictureActions(getPipParams(false));
+                    playbackState = PlaybackState.PAUSED;
+                }
                 break;
             case "mediaControlStopped":
-                updatePictureInPictureActions(getPipParams(false));
+                if (!isMediaPlayingForCurrentTab()) {
+                    updatePictureInPictureActions(getPipParams(false));
+                    playbackState = PlaybackState.STOPPED;
+                }
                 break;
             default:
                 Log.w(LOGTAG, String.format("Unknown new media status: %s", newMediaStatus));