[aw] Add a feature to reset the draw functor in background.

When a WebView becomes invisible, the tiles required for the next frame
are still retained, for as long as the WebView is alive. In particular,
unlocked compositor frame reclaim doesn't work for WebView, contrary to
Chrome.

In practice, this means that we retain ~17MiB of tiles for each
fullscreen WebView which exists on a given device at a time (for a 1440p
device, here on Pixel 6 Pro). A solution to not keep this memory is to
release the draw functor after some time in background. This triggers a
context destroyed notification (DrawFn_OnContextDestroyed), resulting in
SkiaOutputSurfaceImpl getting destroyed, and then all tiles being
released.

Bug: 1424346
Change-Id: I408a040bf1faf4cd6f74bbbcb9d425fa37d87f7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4570622
Reviewed-by: Bo Liu <boliu@chromium.org>
Commit-Queue: Benoit Lize <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1153750}