Onion soup content/renderer/media_capture_from_element/html_video_element_capturer_source.cc

This CL is the second step to Onion soup
content/renderer/media_capture_from_element/. At this time,
html_video_element_capturer_source.cc|h|unittest are moved.

It was preceded by the following preparation CLs [1], [2] and [3].

[1] crrev.com/c/1612104
[2] crrev.com/c/1611781
[3] crrev.com/c/1617324

Notes:

- CL moves media::AddVideoTrackToMediaStream() to be a helper function
  in /blink/renderer/modules/mediacapturefromelement/html_media_element_capture.cc.
  Reason: It was only used there.
- After Onion souping html_video_element_capturer_source.cc, the CL removes
  the respective blink::Platform::CreateHTMLVideoElementCapturer hook.
- Some banned base::Bind calls were replaced by their respective Blink
  counterparts.
- The use of base::GenerateGUID was replaced by Blink's
  CreateCanonicalUUIDString.
- Use of ScopedTaskEnvironment is not needed anymore, hence removed.

BUG=787261,714018

Change-Id: Ia9f040d7477fedebb3497bcb35fc08de191ef73b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1617325
Reviewed-by: Camille Lamy <clamy@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#661332}
16 files changed