Set session stack active state based on the window visibility

app/src/common/shared/org/mozilla/vrbrowser/VRBrowserActivity.java

@@ -336,8 +336,6 @@ protected void onPause() {
         }
         mAudioEngine.pauseEngine();
 
-        SessionStore.get().onPause();
-
         mWindows.onPause();
 
         for (Widget widget: mWidgets.values()) {
@@ -360,7 +358,7 @@ protected void onResume() {
             mOffscreenDisplay.onResume();
         }
 
-        SessionStore.get().onResume();
+        mWindows.onResume();
 
         mAudioEngine.resumeEngine();
         for (Widget widget: mWidgets.values()) {

app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/WindowWidget.java

@@ -239,6 +239,20 @@ protected void onDismiss() {
         }
     }
 
+    @Override
+    public void onPause() {
+        super.onPause();
+        mSessionStack.setActive(false);
+    }
+
+    @Override
+    public void onResume() {
+        super.onResume();
+        if (isVisible()) {
+            mSessionStack.setActive(true);
+        }
+    }
+
     public void close() {
         TelemetryWrapper.closeWindowEvent(mWindowId);
 
@@ -820,6 +834,7 @@ public void setVisible(boolean aVisible) {
         if (mWidgetPlacement.visible == aVisible) {
             return;
         }
+        mSessionStack.setActive(aVisible);
         mWidgetPlacement.visible = aVisible;
         if (!aVisible) {
             if (mIsBookmarksVisible || mIsHistoryVisible) {

app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/Windows.java

@@ -360,6 +360,21 @@ public void resumeCompositor() {
 
     public void onPause() {
         saveState();
+        for (WindowWidget window: mRegularWindows) {
+            window.onPause();
+        }
+        for (WindowWidget window: mPrivateWindows) {
+            window.onPause();
+        }
+    }
+
+    public void onResume() {
+        for (WindowWidget window: mRegularWindows) {
+            window.onResume();
+        }
+        for (WindowWidget window: mPrivateWindows) {
+            window.onResume();
+        }
     }
 
     public void onDestroy() {