Fix MobileHarness playback tests.

This change fixes various issues:
 - MobileHarness sometimes allocated devices with SDK < 16. As we have no tests running
   on these SDKs, a new dimension filter for the mobile_test target ensures that only
   devices with SDK >= 16 are selected. A similar filter for SDK version is also added
   to the ABR playback tests to ensure no old devices are selected.
 - DRM specific tests are skipped for Api < 18, but were not able to run because the
   DashTestRunner class tried to link to the MediaDrm constructor. Moved the
   constructor to a seperate Builder class to allow execution on Api levels 16 and 17.
 - DashWidevineOfflineTest also tried to access code for Api >= 18 without checking
   the current level.
 - Action implementations which are waiting for events did not ensure that they have a
   nextAction to wait for. This caused NullPointerExceptions when this next action was
   scheduled.
 - DefaultDrmSession always restored the offline keys when a new license was requested,
   even if the keys were already restored. These repeated slow calls to restoreKeys
   resulted in high numbers of dropped buffers.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171974859

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

@@ -296,8 +296,7 @@ import java.util.UUID;
       case DefaultDrmSessionManager.MODE_QUERY:
         if (offlineLicenseKeySetId == null) {
           postKeyRequest(ExoMediaDrm.KEY_TYPE_STREAMING, allowRetry);
-        } else {
+        } else if (state == STATE_OPENED_WITH_KEYS || restoreKeys()) {
-          if (restoreKeys()) {
           long licenseDurationRemainingSec = getLicenseDurationRemainingSec();
           if (mode == DefaultDrmSessionManager.MODE_PLAYBACK
               && licenseDurationRemainingSec <= MAX_LICENSE_DURATION_TO_RENEW) {
@@ -318,7 +317,6 @@ import java.util.UUID;
             }
           }
         }
-        }
         break;
       case DefaultDrmSessionManager.MODE_DOWNLOAD:
         if (offlineLicenseKeySetId == null) {

playbacktests/src/androidTest/java/com/google/android/exoplayer2/playbacktests/gts/DashTestRunner.java

@@ -108,22 +108,24 @@ public final class DashTestRunner {
   private String widevineLicenseUrl;
   private DataSource.Factory dataSourceFactory;
 
-  @TargetApi(18)
   @SuppressWarnings("ResourceType")
   public static boolean isL1WidevineAvailable(String mimeType) {
+    if (Util.SDK_INT >= 18) {
       try {
         // Force L3 if secure decoder is not available.
         if (MediaCodecUtil.getDecoderInfo(mimeType, true) == null) {
           return false;
         }
-      MediaDrm mediaDrm = new MediaDrm(WIDEVINE_UUID);
+        MediaDrm mediaDrm = MediaDrmBuilder.build();
         String securityProperty = mediaDrm.getPropertyString(SECURITY_LEVEL_PROPERTY);
         mediaDrm.release();
         return WIDEVINE_SECURITY_LEVEL_1.equals(securityProperty);
-    } catch (MediaCodecUtil.DecoderQueryException | UnsupportedSchemeException e) {
+      } catch (MediaCodecUtil.DecoderQueryException e) {
         throw new IllegalStateException(e);
       }
     }
+    return false;
+  }
 
   public DashTestRunner(String tag, HostActivity activity, Instrumentation instrumentation) {
     this.tag = tag;
@@ -457,4 +459,21 @@ public final class DashTestRunner {
 
   }
 
+  /**
+   * Creates a new {@code MediaDrm} object. The encapsulation ensures that the tests can be
+   * executed for API level < 18.
+   */
+  @TargetApi(18)
+  private static final class MediaDrmBuilder {
+
+    public static MediaDrm build () {
+      try {
+        return new MediaDrm(WIDEVINE_UUID);
+      } catch (UnsupportedSchemeException e) {
+        throw new IllegalStateException(e);
+      }
+    }
+
+  }
+
 }

playbacktests/src/androidTest/java/com/google/android/exoplayer2/playbacktests/gts/DashWidevineOfflineTest.java

@@ -67,9 +67,11 @@ public final class DashWidevineOfflineTest extends ActivityInstrumentationTestCa
     boolean useL1Widevine = DashTestRunner.isL1WidevineAvailable(MimeTypes.VIDEO_H264);
     String widevineLicenseUrl = DashTestData.getWidevineLicenseUrl(true, useL1Widevine);
     httpDataSourceFactory = new DefaultHttpDataSourceFactory(USER_AGENT);
+    if (Util.SDK_INT >= 18) {
       offlineLicenseHelper = OfflineLicenseHelper.newWidevineInstance(widevineLicenseUrl,
           httpDataSourceFactory);
     }
+  }
 
   @Override
   protected void tearDown() throws Exception {

testutils/src/main/java/com/google/android/exoplayer2/testutil/Action.java

@@ -322,6 +322,9 @@ public abstract class Action {
     protected void doActionAndScheduleNextImpl(final SimpleExoPlayer player,
         final MappingTrackSelector trackSelector, final Surface surface, final Handler handler,
         final ActionNode nextAction) {
+      if (nextAction == null) {
+        return;
+      }
       Player.EventListener listener = new Player.DefaultEventListener() {
         @Override
         public void onTimelineChanged(Timeline timeline, Object manifest) {
@@ -362,6 +365,9 @@ public abstract class Action {
     protected void doActionAndScheduleNextImpl(final SimpleExoPlayer player,
         final MappingTrackSelector trackSelector, final Surface surface, final Handler handler,
         final ActionNode nextAction) {
+      if (nextAction == null) {
+        return;
+      }
       player.addListener(new Player.DefaultEventListener() {
         @Override
         public void onPositionDiscontinuity(@Player.DiscontinuityReason int reason) {
@@ -399,6 +405,9 @@ public abstract class Action {
     protected void doActionAndScheduleNextImpl(final SimpleExoPlayer player,
         final MappingTrackSelector trackSelector, final Surface surface, final Handler handler,
         final ActionNode nextAction) {
+      if (nextAction == null) {
+        return;
+      }
       if (targetPlaybackState == player.getPlaybackState()) {
         nextAction.schedule(player, trackSelector, surface, handler);
       } else {
@@ -438,6 +447,9 @@ public abstract class Action {
     protected void doActionAndScheduleNextImpl(final SimpleExoPlayer player,
         final MappingTrackSelector trackSelector, final Surface surface, final Handler handler,
         final ActionNode nextAction) {
+      if (nextAction == null) {
+        return;
+      }
       player.addListener(new Player.DefaultEventListener() {
         @Override
         public void onSeekProcessed() {