media: Use new wrapper types for media mojo interfaces

media/mojo/interfaces/provision_fetcher.mojom

Index: media/mojo/interfaces/provision_fetcher.mojom
diff --git a/media/mojo/interfaces/provision_fetcher.mojom b/media/mojo/interfaces/provision_fetcher.mojom
index 6ea0680c83a6b92ebc015e8d8d8b522bf0d05405..f1e1d814a6a7a3820208fcdc552cdc761e376209 100644
--- a/media/mojo/interfaces/provision_fetcher.mojom
+++ b/media/mojo/interfaces/provision_fetcher.mojom
@@ -12,7 +12,7 @@ interface ProvisionFetcher {
   // Requests the provision information with |default_url| and |request_data|
   // and returns |result| and the |response|. The input parameters |default_url|
   // and |request_data| corresponds to Java class MediaDrm.ProvisionRequest.
-  // |response| will be null iff |result| is false.
+  // |response| will be empty iff |result| is false.
   Retrieve(string default_url, string request_data)
-      => (bool result, string? response);
-};
+      => (bool result, string response);
+};