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

content/renderer/BUILD.gn

Index: content/renderer/BUILD.gn
diff --git a/content/renderer/BUILD.gn b/content/renderer/BUILD.gn
index c4f4510c254808ba2a7d3072fbb49d7afc58058b..c3f15cee564dd4118eb5bb420adc84d21d6d8888 100644
--- a/content/renderer/BUILD.gn
+++ b/content/renderer/BUILD.gn
@@ -4,7 +4,6 @@
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
-import("//build/buildflag_header.gni")
 import("//content/renderer/renderer.gni")
 import("//media/media_options.gni")
 import("//third_party/webrtc/build/webrtc.gni")
@@ -26,7 +25,6 @@ source_set("renderer") {
   defines = []
 
   deps = [
-    ":renderer_features",
     "//base:i18n",
     "//cc",
     "//cc/blink",
@@ -40,6 +38,7 @@ source_set("renderer") {
     "//content/common:mojo_bindings",
     "//content/public/child:child_sources",
     "//content/public/common:common_sources",
+    "//content/public/common:feature_h264_with_openh264_ffmpeg",
     "//content/public/common:mojo_bindings",
     "//crypto:platform",
     "//device/battery:mojo_bindings",
@@ -175,6 +174,9 @@ source_set("renderer") {
       "media/webrtc_logging_noop.cc",
     ]
   }
+  if (rtc_use_h264) {
+    defines += [ "BUILDFLAG_RTC_USE_H264" ]
+  }
 
   if (enable_plugins) {
     sources += rebase_path(
@@ -244,9 +246,3 @@ source_set("renderer") {
     deps += [ "//ui/ozone" ]
   }
 }
-
-buildflag_header("renderer_features") {
-  header = "renderer_features.h"
-
-  flags = [ "RTC_USE_H264=$rtc_use_h264" ]
-}