make use of media_use_ffmpeg in BUILD.gn

Review URL: https://codereview.chromium.org/1297583004

Cr-Commit-Position: refs/heads/master@{#344525}

diff --git a/BUILD.gn b/BUILD.gn
index ff9c0be..511e21f9 100644
--- a/BUILD.gn
+++ b/BUILD.gn

@@ -12,6 +12,7 @@
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/module_args/v8.gni")
+import("//media/media_options.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
@@ -390,7 +391,6 @@
       "//gpu:gpu_perftests",
       "//gpu:gl_tests",
       "//ipc:ipc_perftests",
-      "//media:ffmpeg_regression_tests",  # TODO(GYP) this should be conditional on media_use_ffmpeg
       "//media:media_perftests",
       "//media/cast:generate_barcode_video",
       "//media/cast:generate_timecode_audio",
@@ -426,6 +426,10 @@
       deps += [ "//remoting:remoting_key_tester" ]
     }
 
+    if (media_use_ffmpeg) {
+      deps += [ "//media:ffmpeg_regression_tests" ]
+    }
+
     if (use_ash) {
       deps += [
         "//ash:ash_shell",