Update EME polyfills setServerCertificate to spec

The method should return a Promise resolved with false if unsupported.

Change-Id: I304f2566fc2cf6521eb35f963d7c862e3eca1f48

lib/media/drm_engine.js

@@ -279,8 +279,12 @@ shaka.media.DrmEngine.prototype.attach = function(video) {
   var setServerCertificate = null;
   if (this.currentDrmInfo_.serverCertificate) {
     setServerCertificate = this.mediaKeys_.setServerCertificate(
-        this.currentDrmInfo_.serverCertificate);
-    setServerCertificate = setServerCertificate.catch(function(exception) {
+        this.currentDrmInfo_.serverCertificate).then(function(supported) {
+      if (!supported) {
+        shaka.log.warning('Server certificates are not supported by the key' +
+                          ' system.  The server certificate has been ignored.');
+      }
+    }).catch(function(exception) {
       return Promise.reject(new shaka.util.Error(
           shaka.util.Error.Severity.CRITICAL,
           shaka.util.Error.Category.DRM,

lib/polyfill/patchedmediakeys_ms.js

@@ -299,8 +299,7 @@ shaka.polyfill.PatchedMediaKeysMs.MediaKeys.prototype.
   shaka.log.debug('PatchedMediaKeysMs.MediaKeys.setServerCertificate');
 
   // There is no equivalent in PatchedMediaKeysMs, so return failure.
-  return Promise.reject(new Error('setServerCertificate not supported on ' +
-      'this platform.'));
+  return Promise.resolve(false);
 };
 
 

lib/polyfill/patchedmediakeys_webkit.js

@@ -424,8 +424,7 @@ shaka.polyfill.PatchedMediaKeysWebkit.MediaKeys.prototype.setServerCertificate =
   shaka.log.debug('PatchedMediaKeysWebkit.MediaKeys.setServerCertificate');
 
   // There is no equivalent in v0.1b, so return failure.
-  return Promise.reject(new Error(
-      'setServerCertificate not supported on this platform.'));
+  return Promise.resolve(false);
 };