Ensure that tab dialog and it's surface are invalidated before they are shown (#2179)

Author: MortimerGoro

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

@@ -157,14 +157,15 @@ public void releaseWidget() {
     public void show(int aShowFlags) {
         super.show(aShowFlags);
         refreshTabs();
+        invalidate();
         mWidgetManager.pushWorldBrightness(this, WidgetManagerDelegate.DEFAULT_DIM_BRIGHTNESS);
         mTabsList.requestFocusFromTouch();
     }
 
     @Override
     public void hide(@HideFlags int aHideFlags) {
         super.hide(aHideFlags);
-
+        mRenderer.clearSurface();
         mWidgetManager.popWorldBrightness(this);
     }
 

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

@@ -79,6 +79,11 @@ void drawEnd() {
         mSurfaceCanvas = null;
     }
 
+    void clearSurface() {
+        drawBegin();
+        drawEnd();
+    }
+
     int width() {
         return mTextureWidth;
     }