Make sure vp9 actually gets excluded in gn as well.

webrtc/modules/video_coding/BUILD.gn

Index: webrtc/modules/video_coding/BUILD.gn
diff --git a/webrtc/modules/video_coding/BUILD.gn b/webrtc/modules/video_coding/BUILD.gn
index 21539a2a8fad640f54d30ae325a703bc32677a58..45ff5a700485cbd53d504756a6903d9072abb7d5 100644
--- a/webrtc/modules/video_coding/BUILD.gn
+++ b/webrtc/modules/video_coding/BUILD.gn
@@ -279,15 +279,21 @@ rtc_static_library("webrtc_vp8") {
 }
 
 rtc_static_library("webrtc_vp9") {
-  sources = [
-    "codecs/vp9/include/vp9.h",
-    "codecs/vp9/screenshare_layers.cc",
-    "codecs/vp9/screenshare_layers.h",
-    "codecs/vp9/vp9_frame_buffer_pool.cc",
-    "codecs/vp9/vp9_frame_buffer_pool.h",
-    "codecs/vp9/vp9_impl.cc",
-    "codecs/vp9/vp9_impl.h",
-  ]
+  if (rtc_libvpx_build_vp9) {
+    sources = [
+      "codecs/vp9/include/vp9.h",
+      "codecs/vp9/screenshare_layers.cc",
+      "codecs/vp9/screenshare_layers.h",
+      "codecs/vp9/vp9_frame_buffer_pool.cc",
+      "codecs/vp9/vp9_frame_buffer_pool.h",
+      "codecs/vp9/vp9_impl.cc",
+      "codecs/vp9/vp9_impl.h",
+    ]
+  } else {
+    sources = [
+      "codecs/vp9/vp9_noop.cc",
+    ]
+  }
 
   if (is_clang) {
     # Suppress warnings from Chrome's Clang plugins.