test: Fix filtering of DRM tests by key system

When we turned on MediaCapabilities by default, a check for supported
key systems was removed from one of our tests.  This fixes it by
adding the check back in.

Change-Id: I3a90183b7dbaa40ed98c36a02b1baad31de40d6e

test/media/drm_engine_integration.js

@@ -174,7 +174,7 @@ describe('DrmEngine', () => {
     return support['com.widevine.alpha'] || support['com.microsoft.playready'];
   }
 
-  describe('basic flow', () => {
+  filterDescribe('basic flow', checkSupport, () => {
     drmIt('gets a license and can play encrypted segments', async () => {
       // The error callback should not be invoked.
       onErrorSpy.and.callFake(fail);