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This is a first step to OnionSoup content/renderer/media_capture_from_element/.

It summary, this CL

- Moves content/renderer/media_capture_from_element/canvas_capture_handler* to
  third_party/blink/renderer/modules/mediacapturefromelement/.
- Adapts the existing code for Blink restrictions, eg use WTF::Bind
  instead of base::Bind.
- Removes the code that used to plumb the creation of
  content::CanvasCaptureHandler instances through blink::Platform, and make
  blink::HTMLCanvasElementCapture to create it (see the second TODO
  below).

To be done (follow up CLs):

- migrate some remaining base::Bind{Once,Repeating} uses to the
  respective Blink/WTF alternatives. This is now blocked on having
  a CrossThreadBindOnce implementation available (see
  crrev.com/c/1597228).
- eliminate blink::WebCanvasCaptureHandler
  third_party/blink/public/platform/web_canvas_capture_handler.h.
  Note that this is not done now because there is code in
  third_party/blink/renderer/core/html/canvas/canvas_draw_listener.cc|h
  that use blink::WebCanvasCaptureHandler, and can not use
  blink::CanvasCaptureHandler directly, because core/ can not depend on
  modules/.

R=kentaro@chromium.org, guidou@chromium.org

BUG=787261

Change-Id: Id2dc1f6441e2568c8420f0849a2cb5f87f9a6d75
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1600898Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#658376}