Revert "use navigator.sendBeacon when available"

This reverts commit 48b8035.
Fix #10

Author: steren

stackdriver-errors.js

@@ -118,23 +118,16 @@
 
   StackdriverErrorReporter.prototype.sendErrorPayload = function(payload, callback) {
     var url = baseAPIUrl + this.projectId + "/events:report?key=" + this.apiKey;
-    var CONTENT_TYPE = 'application/json; charset=UTF-8';
-    var payloadString = JSON.stringify(payload);
-    var end = typeof callback === 'function' ? callback : function () {};
-
-    // Check if we can use sendBeacon
-    if (typeof Blob !== 'undefined' && typeof navigator.sendBeacon === 'function') {
-      // create blob to set content type to JSON - needed for correct HTTP header
-      var blob = new Blob([payloadString], { type: CONTENT_TYPE });
-      navigator.sendBeacon(url, blob);
-      return end();
-    }
 
     var xhr = new XMLHttpRequest();
     xhr.open('POST', url, true);
-    xhr.setRequestHeader('Content-Type', CONTENT_TYPE);
-    xhr.onloadend = end;
-    xhr.onerror = end;
-    xhr.send(payloadString);
+    xhr.setRequestHeader('Content-Type', 'application/json; charset=UTF-8');
+    xhr.onloadend = function() {
+      return typeof callback === 'function' && callback();
+    };
+    xhr.onerror = function(e) {
+      return typeof callback === 'function' && callback(e);
+    };
+    xhr.send(JSON.stringify(payload));
   };
 })(this);