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

content/public/common/feature_h264_with_openh264_ffmpeg.h

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_PUBLIC_COMMON_FEATURE_H264_WITH_OPENH264_FFMPEG_H_
+#define CONTENT_PUBLIC_COMMON_FEATURE_H264_WITH_OPENH264_FFMPEG_H_
+
+#include "base/feature_list.h"
+#include "content/public/common/common_features.h"
+
+namespace content {
+
+#if BUILDFLAG(RTC_USE_H264)
+
+// Run-time feature for the |rtc_use_h264| encoder/decoder.
+extern const base::Feature kWebRtcH264WithOpenH264FFmpeg;
+
+#endif  // BUILDFLAG(RTC_USE_H264)
+
+} // namespace content
+
+#endif  // CONTENT_PUBLIC_COMMON_FEATURE_H264_WITH_OPENH264_FFMPEG_H_