Don't attempt license request when keys expire.

- Keys should not expire during normal playbacks of correctly configured content.
- Attempting to refresh on expiration causes a race condition, that may result
  in either failure or brief re-buffer, for the 30s license test video.
- This change provides deterministic behavior, which is to always fail.

demo/src/main/java/com/google/android/exoplayer/demo/Samples.java

@@ -103,7 +103,7 @@ import java.util.Locale;
         + "as=fmp4_audio_cenc,fmp4_sd_hd_cenc&sparams=ip,ipbits,expire,as&ip=0.0.0.0&ipbits=0"
         + "&expire=19000000000&signature=61611F115EEEC7BADE5536827343FFFE2D83D14F."
         + "2FDF4BFA502FB5865C5C86401314BDDEA4799BD0&key=ik0", DemoUtil.TYPE_DASH),
-    new Sample("WV: 30s license duration", "f9a34cab7b05881a",
+    new Sample("WV: 30s license duration (fails at ~30s)", "f9a34cab7b05881a",
         "http://www.youtube.com/api/manifest/dash/id/f9a34cab7b05881a/source/youtube?"
         + "as=fmp4_audio_cenc,fmp4_sd_hd_cenc&sparams=ip,ipbits,expire,as&ip=0.0.0.0&ipbits=0"
         + "&expire=19000000000&signature=88DC53943385CED8CF9F37ADD9E9843E3BF621E6."

library/src/main/java/com/google/android/exoplayer/drm/KeysExpiredException.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer.drm;
+
+/**
+ * Thrown when the drm keys loaded into an open session expire.
+ */
+public final class KeysExpiredException extends Exception {
+}

library/src/main/java/com/google/android/exoplayer/drm/StreamingDrmSessionManager.java

@@ -322,7 +322,7 @@ public class StreamingDrmSessionManager implements DrmSessionManager {
           return;
         case MediaDrm.EVENT_KEY_EXPIRED:
           state = STATE_OPENED;
-          postKeyRequest();
+          onError(new KeysExpiredException());
           return;
         case MediaDrm.EVENT_PROVISION_REQUIRED:
           state = STATE_OPENED;