Support desktop media pipeline on Android for GN build.

media/cdm/ppapi/BUILD.gn

Index: media/cdm/ppapi/BUILD.gn
diff --git a/media/cdm/ppapi/BUILD.gn b/media/cdm/ppapi/BUILD.gn
index 1fdebd1bc75ddff33b437eda0aad03a802c5bac2..b6b2dec79c847f1723df572d6d5fd0c9ea656f3b 100644
--- a/media/cdm/ppapi/BUILD.gn
+++ b/media/cdm/ppapi/BUILD.gn
@@ -5,9 +5,7 @@
 import("//build/config/features.gni")
 import("//chrome/version.gni")  # TODO layering violation!
 import("//media/cdm/ppapi/cdm_adapter.gni")
-
-# Android doesn't use ffmpeg.
-use_ffmpeg = !is_android
+import("//media/media_options.gni")
 
 # The GYP version supports build flags "use_fake_video_decoder" and
 # "use_vpx". These should be added here if necessary but its not clear if
@@ -36,7 +34,7 @@ shared_library("clearkeycdm") {
     "//url",
   ]
 
-  if (use_ffmpeg) {
+  if (media_use_ffmpeg) {
     sources += [
       "external_clear_key/ffmpeg_cdm_audio_decoder.cc",
       "external_clear_key/ffmpeg_cdm_audio_decoder.h",