Make content_shell link in the GN build.

build/config/features.gni

Index: build/config/features.gni
diff --git a/build/config/features.gni b/build/config/features.gni
index a78d30f7648ccb70672990b52baf4066795f5aec..dfa964ce5842f065d281c907b50041fab70e31b8 100644
--- a/build/config/features.gni
+++ b/build/config/features.gni
@@ -29,6 +29,11 @@ declare_args() {
   # resources.pak. It is still possible to load JS files from disk by passing
   # --debug-devtools cmdline switch.
   debug_devtools = false
+
+  # Enables WebRTC.
+  #enable_webrtc = !is_ios  TODO(GYP) use this condition when WebRTC works in
+  #                         the GN build.
+  enable_webrtc = false
 }
 
 # Additional dependent variables -----------------------------------------------
@@ -68,8 +73,6 @@ if (is_android) {
 use_seccomp_bpf = (is_linux || is_android) &&
   (cpu_arch == "x86" || cpu_arch == "x64" || cpu_arch == "arm")
 
-enable_webrtc = !is_ios
-
 # Enable notifications everywhere except Android/iOS.
 # Android is http://crbug.com/115320
 enable_notifications = !is_android && !is_ios