ContentCapture: re-stream onscreen content when the frame show again

Previously ContentCaptureConsumer had no way to know the the frame
shows again because the visible content didn't change.

This patch resets the task session when the frame was hidden, so
ContentCapture task will stream on-screen content because they
aren't streamed from the task point of view when the frame was
shown.

Adds the test to coverage this scenario.

Bug: 1137463
Change-Id: I0065ce080101d2149622b0f9f6a3aa196c18d717
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2511030


Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Michael Bai <michaelbai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823251}