GN: Replace Windows suppressions of warning 4267 with config.

webrtc/modules/bitrate_controller/BUILD.gn

Index: webrtc/modules/bitrate_controller/BUILD.gn
diff --git a/webrtc/modules/bitrate_controller/BUILD.gn b/webrtc/modules/bitrate_controller/BUILD.gn
index 5e3741ba933db058e77b5c9434d20ced72aa82cf..029f54170fa241fdc9e7bcc8b5d618f9ecf3c877 100644
--- a/webrtc/modules/bitrate_controller/BUILD.gn
+++ b/webrtc/modules/bitrate_controller/BUILD.gn
@@ -18,16 +18,12 @@ source_set("bitrate_controller") {
     "send_side_bandwidth_estimation.h",
   ]
 
-  if (is_win) {
-    cflags = [
-      # TODO(jschuh): Bug 1348: fix this warning.
-      "/wd4267",  # size_t to int truncations
-    ]
-  }
-
   configs += [ "../..:common_config" ]
   public_configs = [ "../..:common_inherited_config" ]
 
+  # TODO(jschuh): Bug 1348: fix this warning.
+  configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
+
   if (is_clang) {
     # Suppress warnings from Chrome's Clang plugins.
     # See http://code.google.com/p/webrtc/issues/detail?id=163 for details.