This is the preparation work for multi-window able to render all windows at the same time.
Current compositor can only render one window at the moment.
This PR set all window to the same document ID for now.
We will try to improve webrender upstream to support multi-document rendering for next step.
This is the preparation work for multi-window able to render all windows at the same time. Current compositor can only render one window at the moment. This PR set all window to the same document ID for now. We will try to improve webrender upstream to support multi-document rendering for next step.