Mirroring service refactoring: Add video capture host implementation.

This CL adds a media::mojom::VideoCaptureHost implementation that can
proxy between a single video capture device and a single consumer.

Moved the VideoCaptureDeviceLauncher interface from content/browser/
to content/public/browser so that it can be used by the added
implementation.

Bug: 734672
Change-Id: Id02dfc6a762a3eaac708794766d2a7a2bfee6ee1
Reviewed-on: https://chromium-review.googlesource.com/888199
Commit-Queue: Xiangjun Zhang <[email protected]>
Reviewed-by: Yuri Wiitala <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Reviewed-by: Nico Weber <[email protected]>
Reviewed-by: Christian Fremerey <[email protected]>
Cr-Commit-Position: refs/heads/master@{#535117}
diff --git a/chrome/browser/DEPS b/chrome/browser/DEPS
index 64fba3f3..a46fe308 100644
--- a/chrome/browser/DEPS
+++ b/chrome/browser/DEPS
@@ -42,6 +42,7 @@
   "+media/audio", # For media audio hang monitor.
   "+media/base",  # For media switches
   "+media/cdm/cdm_paths.h",
+  "+media/capture",
   "+media/midi",  # For midi switches
   "+media/mojo",  # For mojo media services.
   "+ppapi/c",  # For various types.