Updated XHR API so call sites are more descriptive.

remoting/webapp/crd/js/host_controller.js

Index: remoting/webapp/crd/js/host_controller.js
diff --git a/remoting/webapp/crd/js/host_controller.js b/remoting/webapp/crd/js/host_controller.js
index 3dd8c93558c8d489aa53b8cb9fe2a97724bbc848..7a086fcc243b2f24845f2b94450bfd45bea810e8 100644
--- a/remoting/webapp/crd/js/host_controller.js
+++ b/remoting/webapp/crd/js/host_controller.js
@@ -273,11 +273,6 @@ remoting.HostController.prototype.start = function(hostPin, consent, onDone,
    */
   function doRegisterHost(
       hostName, privateKey, publicKey, hostClientId, oauthToken) {
-    var headers = {
-      'Authorization': 'OAuth ' + oauthToken,
-      'Content-type' : 'application/json; charset=UTF-8'
-    };
-
     var newHostDetails = { data: {
        hostId: newHostId,
        hostName: hostName,
@@ -287,16 +282,16 @@ remoting.HostController.prototype.start = function(hostPin, consent, onDone,
     var registerHostUrl =
         remoting.settings.DIRECTORY_API_BASE_URL + '/@me/hosts';
 
-    if (hostClientId) {

[Jamie, 2015/02/21 01:35:48]

You've deleted this conditional. Was that intentional?

[John Williams, 2015/02/23 23:00:55]

Yes. The new version automagically omits URL parameters and headers whose value
is null.  I suppose line 289 in the new code should say "hostClientId || null"
to ensure the semantics haven't changed, but the type annotations led me to
believe hostClientId will always be truthy or null.

Omitting null fields feels somewhat magical to me, but it's a pattern I've used
a lot in the past, and I've always found the result easier to read than having
conditional logic at the call site.

-      registerHostUrl += '?' + remoting.xhr.urlencodeParamHash(
-          { hostClientId: hostClientId });
-    }
-
-    remoting.xhr.post(
-        registerHostUrl,
-        onRegistered.bind(null, hostName, publicKey, privateKey),
-        JSON.stringify(newHostDetails),
-        headers);
+    remoting.xhr.start({
+      method: 'POST',
+      url: remoting.settings.DIRECTORY_API_BASE_URL + '/@me/hosts',
+      urlParams: {
+        hostClientId: hostClientId
+      },
+      onDone: onRegistered.bind(null, hostName, publicKey, privateKey),
+      jsonContent: newHostDetails,
+      oauthToken: oauthToken
+    });
   }
 
   /**