Remove Unnecessary Delay

This removes an unnecessary delay in the Telemetry code that caused
the code to wait an extra minute before trying to send data per page
load.

This also adds logic so that the code will wait until any previous
attempt to send telemetry causes follow-up attempts to wait until
it has completed sending (in the unlikely event that it takes
longer than a minute, we don't want to waste time / resources).

x-pack/plugins/xpack_main/public/hacks/telemetry.js

@@ -23,6 +23,7 @@ export class Telemetry {
     this._telemetryOptedIn = $injector.get('telemetryOptedIn');
     this._attributes = this._storage.get(LOCALSTORAGE_KEY) || {};
     this._fetchTelemetry = fetchTelemetry;
+    this._sending = false;
   }
 
   _set(key, value) {
@@ -57,11 +58,16 @@ export class Telemetry {
     return false;
   }
 
-  /*
+  /**
    * Check report permission and if passes, send the report
+   *
+   * This function never throws an exception.
    */
   _sendIfDue() {
-    if (!this._checkReportStatus()) { return Promise.resolve(null); }
+    if (this._sending || !this._checkReportStatus()) { return Promise.resolve(false); }
+
+    // mark that we are working so future requests are ignored until we're done
+    this._sending = true;
 
     return this._fetchTelemetry()
       .then(response => {
@@ -76,22 +82,22 @@ export class Telemetry {
           return this._$http(req);
         });
       })
-      .then(response => {
+      // the response object is ignored because we do not check it
+      .then(() => {
         // we sent a report, so we need to record and store the current time stamp
         this._set('lastReport', Date.now());
         this._saveToBrowser();
-        return response;
       })
-      .catch(() => {
-        // no ajaxErrorHandlers for telemetry
-        return Promise.resolve(null);
-      });
+      // no ajaxErrorHandlers for telemetry
+      .catch(() => null)
+      .then(() => this._sending = false);
   }
 
-  /*
+  /**
    * Public method
    */
   start() {
+    // continuously check if it's due time for a report
     window.setInterval(() => this._sendIfDue(), 60000);
   }