Don't time-travel when resuming play.

danmaku/GameView.mm

@@ -194,14 +194,13 @@ static NSTimeInterval const FRAME_INTERVAL = 1.0 / 60.0;
   [timer invalidate];
   [frameTimer invalidate];
   
-  // env::pause_clock();
   [self setNeedsDisplay:YES];
 }
 
 - (void)windowDidBecomeMain:(NSNotification *)notification {
   NSLog(@"window did become main");
 
-  // env::resume_clock();
+  game->set_current_timestamp();
   [self setNeedsDisplay:YES];
   
   // TODO (sjaffe): Become able to change framerate