This allows us to keep always some frame around so we can return it
everytime consumer asks us to capture a frame as before we either
returned current frame or nothing as there was no new frame available.
This will be needed in order to support mouse cursor separately as
DesktopAndCursorComposer requires frame everytime, even if it's the
same one as before so we can combine it with the mouse cursor.
Bug: webrtc:13429
Change-Id: Ice87968846870c0a880ab469d9e052b4978e658c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/239362
Reviewed-by: Mark Foltz <mfoltz@chromium.org>
Commit-Queue: Mark Foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#35956}
49e0e77e40