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

WebRtcBrowserTest for H.264.

The compile flag |rtc_use_h264| defaults to
|proprietary_codecs| which is used on some Chromium bots
and in the official Chrome build. The new run-time flag
|kWebRtcH264WithOpenH264FFmpeg| determines if the
|rtc_use_h264| encoder/decoder will be used at runtime.

The run-time flag is off by default.

This CL:
- Adds run-time flag and a new build target for it. It is
placed in content/public/renderer/media/webrtc/ because it
can't/shouldn't be placed in the webrtc repo and
peer_connection_dependency_factory.cc lives in
content/renderer/media/webrtc/.
- Moves renderer_features and its generated header file
target from content/renderer/ to content/public/renderer/
to not break include rules.
- Based on the run-time flag, enables or disables H.264 in
peer_connection_dependency_factory.cc.
- If flag is on, runs a new H.264 browser test.

BUG=chromium:500605, chromium:468365

Review URL: https://codereview.chromium.org/1673183002

Cr-Commit-Position: refs/heads/master@{#376451}

1 files changed, 4 insertions, 1 deletions

diff --git a/content/public/renderer/BUILD.gn b/content/public/renderer/BUILD.gn
index 719eadf..42687cc 100644
--- a/content/public/renderer/BUILD.gn
+++ b/content/public/renderer/BUILD.gn
@@ -49,7 +49,10 @@ source_set("renderer_sources") {
         rebase_path(content_renderer_gypi_values.public_renderer_webrtc_sources,
                     ".",
                     "//content")
-    deps += [ "//third_party/webrtc" ]
+    deps += [
+      "//content/public/common:feature_h264_with_openh264_ffmpeg",
+      "//third_party/webrtc",
+    ]
   }
 
   if (enable_plugins) {