media: Use "public_configs" for "mojo_media_config"

content/renderer/BUILD.gn

Index: content/renderer/BUILD.gn
diff --git a/content/renderer/BUILD.gn b/content/renderer/BUILD.gn
index f9a554d07e7689f9cd199ed8a2dc5df0dfea6884..caa799b97484b97524c0bdcbcafb471e577bec71 100644
--- a/content/renderer/BUILD.gn
+++ b/content/renderer/BUILD.gn
@@ -230,6 +230,8 @@ source_set("renderer") {
 
     deps += [
       "//media/mojo/interfaces",
+
+      # Defines in mojo_media_config are also pulled in here.
       "//media/mojo/services:proxy",
     ]
   }
@@ -255,6 +257,12 @@ source_set("renderer") {
 # See comment at the top of //content/BUILD.gn for how this works.
 group("for_content_tests") {
   visibility = [ "//content/test/*" ]
+
+  if (enable_mojo_media) {
+    # For the defines in mojo_media_config.
+    public_configs = [ "//media/mojo/services:mojo_media_config" ]
+  }
+
   if (!is_component_build) {
     public_deps = [
       ":renderer",