Call DrmSession methods on the session not the manager

The way it was before worked, but it's not really documented
that DrmSession methods implemented by DefaultDrmSessionManager
can be called after the session has been released, and it feels
wrong to do this.

At some point we should probably consider moving the DrmSession
part of DefaultDrmSessionManager into an inner class, to force
usage in the "normal" way.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=151003855

library/core/src/main/java/com/google/android/exoplayer2/drm/OfflineLicenseHelper.java

@@ -133,8 +133,7 @@ public final class OfflineLicenseHelper<T extends ExoMediaCrypto> {
   public synchronized byte[] downloadLicense(DrmInitData drmInitData) throws IOException,
       InterruptedException, DrmSessionException {
     Assertions.checkArgument(drmInitData != null);
-    blockingKeyRequest(DefaultDrmSessionManager.MODE_DOWNLOAD, null, drmInitData);
-    return drmSessionManager.getOfflineLicenseKeySetId();
+    return blockingKeyRequest(DefaultDrmSessionManager.MODE_DOWNLOAD, null, drmInitData);
   }
 
   /**
@@ -147,8 +146,7 @@ public final class OfflineLicenseHelper<T extends ExoMediaCrypto> {
   public synchronized byte[] renewLicense(byte[] offlineLicenseKeySetId)
       throws DrmSessionException {
     Assertions.checkNotNull(offlineLicenseKeySetId);
-    blockingKeyRequest(DefaultDrmSessionManager.MODE_DOWNLOAD, offlineLicenseKeySetId, null);
-    return drmSessionManager.getOfflineLicenseKeySetId();
+    return blockingKeyRequest(DefaultDrmSessionManager.MODE_DOWNLOAD, offlineLicenseKeySetId, null);
   }
 
   /**
@@ -173,34 +171,43 @@ public final class OfflineLicenseHelper<T extends ExoMediaCrypto> {
   public synchronized Pair<Long, Long> getLicenseDurationRemainingSec(byte[] offlineLicenseKeySetId)
       throws DrmSessionException {
     Assertions.checkNotNull(offlineLicenseKeySetId);
-    DrmSession<T> session = openBlockingKeyRequest(DefaultDrmSessionManager.MODE_QUERY,
+    DrmSession<T> drmSession = openBlockingKeyRequest(DefaultDrmSessionManager.MODE_QUERY,
         offlineLicenseKeySetId, null);
+    DrmSessionException error = drmSession.getError();
     Pair<Long, Long> licenseDurationRemainingSec =
-        WidevineUtil.getLicenseDurationRemainingSec(drmSessionManager);
-    drmSessionManager.releaseSession(session);
+        WidevineUtil.getLicenseDurationRemainingSec(drmSession);
+    drmSessionManager.releaseSession(drmSession);
+    if (error != null) {
+      if (error.getCause() instanceof KeysExpiredException) {
+        return Pair.create(0L, 0L);
+      }
+      throw error;
+    }
     return licenseDurationRemainingSec;
   }
 
-  private void blockingKeyRequest(@Mode int licenseMode, byte[] offlineLicenseKeySetId,
+  private byte[] blockingKeyRequest(@Mode int licenseMode, byte[] offlineLicenseKeySetId,
       DrmInitData drmInitData) throws DrmSessionException {
-    DrmSession<T> session = openBlockingKeyRequest(licenseMode, offlineLicenseKeySetId,
+    DrmSession<T> drmSession = openBlockingKeyRequest(licenseMode, offlineLicenseKeySetId,
         drmInitData);
-    DrmSessionException error = session.getError();
+    DrmSessionException error = drmSession.getError();
+    byte[] keySetId = drmSession.getOfflineLicenseKeySetId();
+    drmSessionManager.releaseSession(drmSession);
     if (error != null) {
       throw error;
     }
-    drmSessionManager.releaseSession(session);
+    return keySetId;
   }
 
   private DrmSession<T> openBlockingKeyRequest(@Mode int licenseMode, byte[] offlineLicenseKeySetId,
       DrmInitData drmInitData) {
     drmSessionManager.setMode(licenseMode, offlineLicenseKeySetId);
     conditionVariable.close();
-    DrmSession<T> session = drmSessionManager.acquireSession(handlerThread.getLooper(),
+    DrmSession<T> drmSession = drmSessionManager.acquireSession(handlerThread.getLooper(),
         drmInitData);
     // Block current thread until key loading is finished
     conditionVariable.block();
-    return session;
+    return drmSession;
   }
 
 }