Bug 1427771 - Fix broken exitFullScreen() in GeckoSession and call it in onBackPressed in custom tabs and PWAs. r=snorp

mobile/android/base/java/org/mozilla/gecko/customtabs/CustomTabsActivity.java

@@ -267,10 +267,13 @@ public class CustomTabsActivity extends AppCompatActivity
 
     @Override
     public void onBackPressed() {
-        if (mCanGoBack) {
+        final boolean fullScreen = ActivityUtils.isFullScreen(this);
+        if (fullScreen) {
+            mGeckoSession.exitFullScreen();
+        } else if (mCanGoBack) {
             mGeckoSession.goBack();
         } else {
-            finish();
+            super.onBackPressed();
         }
     }
 

mobile/android/modules/geckoview/GeckoViewContent.jsm

@@ -53,6 +53,8 @@ class GeckoViewContent extends GeckoViewModule {
     debug("onEvent: " + aEvent);
     switch (aEvent) {
       case "GeckoViewContent:ExitFullScreen":
+        this.messageManager.sendAsyncMessage("GeckoView:DOMFullscreenExited");
+        break;
       case "GeckoView:ZoomToInput":
         this.messageManager.sendAsyncMessage(aEvent);
         break;