feat(doit): pre-request delegate call.

This one is likely to change the further we advance in the upload-media
implementation.

src/mako/lib/mbuild.mako

@@ -466,6 +466,9 @@ else {
             }
             let auth_header = hyper::header::Authorization(token.unwrap().access_token);
             % endif
+            if ${delegate}.is_some() {
+                ${delegate_call}.pre_request("${m.id}");
+            }
             match ${client}.request(hyper::method::Method::Extension("${m.httpMethod}".to_string()), url.as_slice())
                .header(hyper::header::UserAgent("google-api-rust-client/${cargo.build_version}".to_string()))
                % if supports_scopes(auth):

src/rust/cmn.rs

@@ -82,6 +82,10 @@ pub trait Delegate {
     fn http_failure(&mut self, _: &hyper::client::Response, JsonServerError) -> oauth2::Retry {
         oauth2::Retry::Abort
     }
+
+    /// Called prior to sending the main request of the given method. It can be used to time 
+    /// the call or to print progress information.
+    fn pre_request(&mut self, method_name: &str) { let _ = method_name; }
 }
 
 #[derive(Default)]