Mojom: Blanket change to mark all pointer/handle fields as nullable.

mojo/services/public/interfaces/launcher/launcher.mojom

Index: mojo/services/public/interfaces/launcher/launcher.mojom
diff --git a/mojo/services/public/interfaces/launcher/launcher.mojom b/mojo/services/public/interfaces/launcher/launcher.mojom
index 839bffb5cfcbf5f85cd6523fdac320c111bdaa17..46f0dccce5f8937ac99f79b8e5592fcc015c9532 100644
--- a/mojo/services/public/interfaces/launcher/launcher.mojom
+++ b/mojo/services/public/interfaces/launcher/launcher.mojom
@@ -23,8 +23,8 @@ interface Launcher {
   //
   // Note: |response| can be NULL in the case where a request was not needed to
   // determine the correct handler.
-  Launch(NavigationDetails details) =>
-      (string handler_url, string view_url, ResponseDetails response);
+  Launch(NavigationDetails? details) =>
+      (string? handler_url, string? view_url, ResponseDetails? response);
 };
 
 }