test: Fix test failures triggered with --no-babel

When we run ./test.py --no-babel, Babel is not used to transpile the
tests.  (This restricts test runs to modern browsers and prevents
testing on, say, IE11.)

But Babel seems to have masked some issues with constructor spies.
Jasmine will call your fake callback with "new" if the spy itself is
called with "new", but this means that constructor spies must have
plain function callbacks, not arrow functions.

Change-Id: I936b024504c4173cc29824408e97e5c7d6c591d8

Author: joeyparrish

test/media/media_source_engine_unit.js

@@ -181,10 +181,15 @@ describe('MediaSourceEngine', () => {
       shaka.media.MediaSourceEngine.createObjectURL =
         Util.spyFunc(createObjectURLSpy);
 
-      const mediaSourceSpy =
-          jasmine.createSpy('MediaSource').and.callFake(() => {
-            return mockMediaSource;
-          });
+      const mediaSourceSpy = jasmine.createSpy('MediaSource');
+      // Because this is a fake constructor, it must be callable with "new".
+      // This will cause jasmine to invoke the callback with "new" as well, so
+      // the callback must be a "function".  This detail is hidden when babel
+      // transpiles the tests.
+      // eslint-disable-next-line prefer-arrow-callback, no-restricted-syntax
+      mediaSourceSpy.and.callFake(function() {
+        return mockMediaSource;
+      });
       window.MediaSource = Util.spyFunc(mediaSourceSpy);
 
       await mediaSourceEngine.destroy();
@@ -1158,7 +1163,12 @@ describe('MediaSourceEngine', () => {
   function createMockTextEngineCtor() {
     const ctor = jasmine.createSpy('TextEngine');
     ctor['isTypeSupported'] = () => true;
-    ctor.and.callFake(() => {
+    // Because this is a fake constructor, it must be callable with "new".
+    // This will cause jasmine to invoke the callback with "new" as well, so
+    // the callback must be a "function".  This detail is hidden when babel
+    // transpiles the tests.
+    // eslint-disable-next-line prefer-arrow-callback, no-restricted-syntax
+    ctor.and.callFake(function() {
       expect(mockTextEngine).toBeFalsy();
       mockTextEngine = jasmine.createSpyObj('TextEngine', [
         'initParser', 'destroy', 'appendBuffer', 'remove', 'setTimestampOffset',