Allow request headers to be set in StackTrace.report()

This adds a 4th Object parameter for request options to
StackTrace.report(). Specifying headers: {} allows one to
customize request headers.

Issue: #168

Author: eriwen

spec/stacktrace-spec.js

@@ -216,8 +216,6 @@ describe('StackTrace', function() {
 
             function callback() {
                 expect(postRequest.data()).toEqual({message: errorMsg, stack: stackframes});
-                expect(postRequest.method).toBe('post');
-                expect(postRequest.url).toBe(url);
                 done();
             }
         });
@@ -246,5 +244,22 @@ describe('StackTrace', function() {
             jasmine.Ajax.stubRequest(url).andError();
             StackTrace.report(stackframes, url).then(done.fail, done)['catch'](done);
         });
+
+        it('allows specification of request headers', function(done) {
+            var url = 'http://domain.ext/endpoint';
+            var stackframes = [new StackFrame({functionName: 'fn', fileName: 'file.js', lineNumber: 32, columnNumber: 1})];
+            var requestOptions = {headers: {'Access-Control-Request-Method': 'POST'}};
+
+            StackTrace.report(stackframes, url, null, requestOptions).then(callback, done.fail)['catch'](done.fail);
+
+            var postRequest = jasmine.Ajax.requests.mostRecent();
+            postRequest.respondWith({status: 201, contentType: 'text/plain', responseText: 'OK'});
+
+            function callback() {
+                expect(postRequest.data()).toEqual({stack: stackframes});
+                expect(postRequest.requestHeaders).toEqual({'Access-Control-Request-Method': 'POST', 'Content-Type': 'application/json'});
+                done();
+            }
+        });
     });
 });

stacktrace.js

@@ -187,8 +187,9 @@
          * @param {Array} stackframes
          * @param {String} url
          * @param {String} errorMsg
+         * @param {Object} requestOptions
          */
-        report: function StackTrace$$report(stackframes, url, errorMsg) {
+        report: function StackTrace$$report(stackframes, url, errorMsg, requestOptions) {
             return new Promise(function(resolve, reject) {
                 var req = new XMLHttpRequest();
                 req.onerror = reject;
@@ -202,10 +203,20 @@
                     }
                 };
                 req.open('post', url);
+
+                // Set request headers
                 req.setRequestHeader('Content-Type', 'application/json');
+                if (requestOptions && typeof requestOptions.headers === 'object') {
+                    var headers = requestOptions.headers;
+                    for (var header in headers) {
+                        if (headers.hasOwnProperty(header)) {
+                            req.setRequestHeader(header, headers[header]);
+                        }
+                    }
+                }
 
                 var reportPayload = {stack: stackframes};
-                if (errorMsg !== undefined) {
+                if (errorMsg !== undefined && errorMsg !== null) {
                     reportPayload.message = errorMsg;
                 }