Enable H.264 video WebRTC behind run-time flag and add WebRtcBrowserTest for H.264

chrome/browser/media/DEPS

Index: chrome/browser/media/DEPS
diff --git a/chrome/browser/media/DEPS b/chrome/browser/media/DEPS
index c230b82f8eee2fa3a405d12f5d2f9bd2097379f9..b323d93c73974c0c909dadc4e07a1279f198def2 100644
--- a/chrome/browser/media/DEPS
+++ b/chrome/browser/media/DEPS
@@ -1,4 +1,5 @@
 include_rules = [
+  "+content/renderer/renderer_features.h",  # For BUILDFLAG(RTC_USE_H264).

[hbos_chromium, 2016/02/08 15:22:53]

|rtc_use_h264| is a build flag from the webrtc repo. BUILDFLAG(RTC_USE_H264)
checks if the flag is set or not (renderer_features.h is auto-generated and
defines it). This would probably typically be placed where the flag is defined,
but because this does not exist in the webrtc repo I defined it closest to where
BUILDFLAG(RTC_USE_H264) is used, which was peer_connection_dependency_factory.cc
in content/renderer/...
  Now that we also use it in unittests, DEPS needed to be updated. This is not
to say that chrome/browser/media now depends on other content/renderer stuff.

[Avi (use Gerrit), 2016/02/09 16:45:03]

No.

content/public is the public API for content. You may not include any file
outside of it.

[hbos_chromium, 2016/02/10 09:48:08]

OK. I made renderer_features.h content/public/ instead. The only "feature" it
defines is the RTC_USE_H264 buildflag, no need for that not to be public.

   "+media/audio",
   "+media/base",
   "+media/cast",