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

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index ff183c6040778e443e0448eefdffe81312f07e3d..200752a683edfe750c6128ca54678943364b2aae 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -10,6 +10,7 @@ import("//build/config/ui.gni")
 import("//chrome/chrome_tests.gni")
 import("//chrome/test/base/js2gtest.gni")
 import("//testing/test.gni")
+import("//third_party/webrtc/build/webrtc.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
@@ -1086,7 +1087,9 @@ if (!is_android) {
     if (enable_captive_portal_detection) {
       sources += [ "../browser/captive_portal/captive_portal_browsertest.cc" ]
     }
-    if (!enable_webrtc) {
+    if (enable_webrtc) {
+      deps += [ "//content/public/common:feature_h264_with_openh264_ffmpeg" ]
+    } else {
       sources -= [
         "../browser/extensions/api/webrtc_audio_private/webrtc_audio_private_browsertest.cc",
         "../browser/extensions/api/webrtc_logging_private/webrtc_logging_private_apitest.cc",
@@ -1095,6 +1098,9 @@ if (!is_android) {
         "../browser/media/chrome_webrtc_getmediadevices_browsertest.cc",
       ]
     }
+    if (rtc_use_h264) {
+      defines += [ "BUILDFLAG_RTC_USE_H264" ]
+    }
     if (enable_media_router) {
       sources += [ "../browser/ui/webui/media_router/media_router_dialog_controller_impl_browsertest.cc" ]
       deps += [ "//chrome/test/media_router:media_router_browsertests" ]