Add analytics listener interface and default data collector.

The data collector keeps track of active media periods to assign each event to
the correct media period and/or window. This information, together with other
information like playback position and buffered duration, is then forwarded
with the event to all registered listeners.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=191726408

library/core/src/main/java/com/google/android/exoplayer2/analytics/DefaultAnalyticsListener.java

+/*
+ * Copyright (C) 2018 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.exoplayer2.analytics;
+
+import android.net.NetworkInfo;
+import android.view.Surface;
+import com.google.android.exoplayer2.ExoPlaybackException;
+import com.google.android.exoplayer2.Format;
+import com.google.android.exoplayer2.PlaybackParameters;
+import com.google.android.exoplayer2.decoder.DecoderCounters;
+import com.google.android.exoplayer2.metadata.Metadata;
+import com.google.android.exoplayer2.source.MediaSourceEventListener.LoadEventInfo;
+import com.google.android.exoplayer2.source.MediaSourceEventListener.MediaLoadData;
+import com.google.android.exoplayer2.source.TrackGroupArray;
+import com.google.android.exoplayer2.trackselection.TrackSelectionArray;
+import java.io.IOException;
+
+/**
+ * {@link AnalyticsListener} allowing selective overrides. All methods are implemented as no-ops.
+ */
+public abstract class DefaultAnalyticsListener implements AnalyticsListener {
+
+  @Override
+  public void onPlayerStateChanged(EventTime eventTime, boolean playWhenReady, int playbackState) {}
+
+  @Override
+  public void onTimelineChanged(EventTime eventTime, int reason) {}
+
+  @Override
+  public void onPositionDiscontinuity(EventTime eventTime, int reason) {}
+
+  @Override
+  public void onSeekStarted(EventTime eventTime) {}
+
+  @Override
+  public void onSeekProcessed(EventTime eventTime) {}
+
+  @Override
+  public void onPlaybackParametersChanged(
+      EventTime eventTime, PlaybackParameters playbackParameters) {}
+
+  @Override
+  public void onRepeatModeChanged(EventTime eventTime, int repeatMode) {}
+
+  @Override
+  public void onShuffleModeChanged(EventTime eventTime, boolean shuffleModeEnabled) {}
+
+  @Override
+  public void onLoadingChanged(EventTime eventTime, boolean isLoading) {}
+
+  @Override
+  public void onPlayerError(EventTime eventTime, ExoPlaybackException error) {}
+
+  @Override
+  public void onTracksChanged(
+      EventTime eventTime, TrackGroupArray trackGroups, TrackSelectionArray trackSelections) {}
+
+  @Override
+  public void onLoadStarted(
+      EventTime eventTime, LoadEventInfo loadEventInfo, MediaLoadData mediaLoadData) {}
+
+  @Override
+  public void onLoadCompleted(
+      EventTime eventTime, LoadEventInfo loadEventInfo, MediaLoadData mediaLoadData) {}
+
+  @Override
+  public void onLoadCanceled(
+      EventTime eventTime, LoadEventInfo loadEventInfo, MediaLoadData mediaLoadData) {}
+
+  @Override
+  public void onLoadError(
+      EventTime eventTime,
+      LoadEventInfo loadEventInfo,
+      MediaLoadData mediaLoadData,
+      IOException error,
+      boolean wasCanceled) {}
+
+  @Override
+  public void onDownstreamFormatChanged(EventTime eventTime, MediaLoadData mediaLoadData) {}
+
+  @Override
+  public void onUpstreamDiscarded(EventTime eventTime, MediaLoadData mediaLoadData) {}
+
+  @Override
+  public void onMediaPeriodCreated(EventTime eventTime) {}
+
+  @Override
+  public void onMediaPeriodReleased(EventTime eventTime) {}
+
+  @Override
+  public void onReadingStarted(EventTime eventTime) {}
+
+  @Override
+  public void onBandwidthEstimate(
+      EventTime eventTime, int totalLoadTimeMs, long totalBytesLoaded, long bitrateEstimate) {}
+
+  @Override
+  public void onViewportSizeChange(EventTime eventTime, int width, int height) {}
+
+  @Override
+  public void onNetworkTypeChanged(EventTime eventTime, NetworkInfo networkInfo) {}
+
+  @Override
+  public void onMetadata(EventTime eventTime, Metadata metadata) {}
+
+  @Override
+  public void onDecoderEnabled(
+      EventTime eventTime, int trackType, DecoderCounters decoderCounters) {}
+
+  @Override
+  public void onDecoderInitialized(
+      EventTime eventTime, int trackType, String decoderName, long initializationDurationMs) {}
+
+  @Override
+  public void onDecoderInputFormatChanged(EventTime eventTime, int trackType, Format format) {}
+
+  @Override
+  public void onDecoderDisabled(
+      EventTime eventTime, int trackType, DecoderCounters decoderCounters) {}
+
+  @Override
+  public void onAudioSessionId(EventTime eventTime, int audioSessionId) {}
+
+  @Override
+  public void onAudioUnderrun(
+      EventTime eventTime, int bufferSize, long bufferSizeMs, long elapsedSinceLastFeedMs) {}
+
+  @Override
+  public void onDroppedVideoFrames(EventTime eventTime, int droppedFrames, long elapsedMs) {}
+
+  @Override
+  public void onVideoSizeChanged(
+      EventTime eventTime,
+      int width,
+      int height,
+      int unappliedRotationDegrees,
+      float pixelWidthHeightRatio) {}
+
+  @Override
+  public void onRenderedFirstFrame(EventTime eventTime, Surface surface) {}
+
+  @Override
+  public void onAdLoadError(EventTime eventTime, IOException error) {}
+
+  @Override
+  public void onInternalAdLoadError(EventTime eventTime, RuntimeException error) {}
+
+  @Override
+  public void onAdClicked(EventTime eventTime) {}
+
+  @Override
+  public void onAdTapped(EventTime eventTime) {}
+
+  @Override
+  public void onDrmKeysLoaded(EventTime eventTime) {}
+
+  @Override
+  public void onDrmSessionManagerError(EventTime eventTime, Exception error) {}
+
+  @Override
+  public void onDrmKeysRestored(EventTime eventTime) {}
+
+  @Override
+  public void onDrmKeysRemoved(EventTime eventTime) {}
+}