This patch fixes two opacity/mask optimizations when WebRender is in use:
- The first optimization defers opacity handling and applies it during painting of nsDisplayMasksAndClipPaths if it is the only item inside nsDisplayOpacity. This was broken because WebRenderCommandBuilder did not invalidate the mask image when this decision changed.
- The second optimization applies opacity directly to stacking context in |nsDisplayMasksAndClipPaths::CreateWebRenderCommands()| with non-polygonal clip-paths. This was relying on the above optimization incorrectly triggering, which flattened away the opacity container. However, if the nsDisplayOpacity was active or contained more than one item, the opacity could be applied twice.
Differential Revision: https://phabricator.services.mozilla.com/D68995
0075ba9551