Correctly handle dynamic playlist modifications

- Fix bug where we'd try and call replaceStream having already
  notified the renderer that the current stream is final. This
  could occur if a period was added to the end of the playlist.
- If the current period being played is removed and a new period
  to play cannot be resolved, assume we've gone off the end of
  the playlist and transition to the ended state. This allows
  the current source to be re-used (unlike the previous behavior
  of considering it an error). Treat valid seeks that cannot be
  resolved due to concurrent timeline update similarly.
- Add seek sanity check back to ExoPlayerImpl. Meh. It's probably
  best to keep this, since it stops the exposed window index
  being invalid w.r.t the exposed timeline.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=141167151

library/src/main/java/com/google/android/exoplayer2/BaseRenderer.java

@@ -107,11 +107,16 @@ public abstract class BaseRenderer implements Renderer, RendererCapabilities {
   }
   }
 
 
   @Override
   @Override
-  public final void setCurrentStreamIsFinal() {
+  public final void setCurrentStreamFinal() {
     streamIsFinal = true;
     streamIsFinal = true;
   }
   }
 
 
   @Override
   @Override
+  public final boolean isCurrentStreamFinal() {
+    return streamIsFinal;
+  }
+
+  @Override
   public final void maybeThrowStreamError() throws IOException {
   public final void maybeThrowStreamError() throws IOException {
     stream.maybeThrowError();
     stream.maybeThrowError();
   }
   }
@@ -243,7 +248,7 @@ public abstract class BaseRenderer implements Renderer, RendererCapabilities {
 
 
   /**
   /**
    * Reads from the enabled upstream source. If the upstream source has been read to the end then
    * Reads from the enabled upstream source. If the upstream source has been read to the end then
-   * {@link C#RESULT_BUFFER_READ} is only returned if {@link #setCurrentStreamIsFinal()} has been
+   * {@link C#RESULT_BUFFER_READ} is only returned if {@link #setCurrentStreamFinal()} has been
    * called. {@link C#RESULT_NOTHING_READ} is returned otherwise.
    * called. {@link C#RESULT_NOTHING_READ} is returned otherwise.
    *
    *
    * @see SampleStream#readData(FormatHolder, DecoderInputBuffer)
    * @see SampleStream#readData(FormatHolder, DecoderInputBuffer)

library/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java

@@ -179,6 +179,9 @@ import java.util.concurrent.CopyOnWriteArraySet;
 
 
   @Override
   @Override
   public void seekTo(int windowIndex, long positionMs) {
   public void seekTo(int windowIndex, long positionMs) {
+    if (windowIndex < 0 || (!timeline.isEmpty() && windowIndex >= timeline.getWindowCount())) {
+      throw new IllegalSeekPositionException(timeline, windowIndex, positionMs);
+    }
     pendingSeekAcks++;
     pendingSeekAcks++;
     maskingWindowIndex = windowIndex;
     maskingWindowIndex = windowIndex;
     if (positionMs == C.TIME_UNSET) {
     if (positionMs == C.TIME_UNSET) {

library/src/main/java/com/google/android/exoplayer2/IllegalSeekPositionException.java

+/*
+ * Copyright (C) 2016 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;
+
+/**
+ * Thrown when an attempt is made to seek to a position that does not exist in the player's
+ * {@link Timeline}.
+ */
+public final class IllegalSeekPositionException extends IllegalStateException {
+
+  /**
+   * The {@link Timeline} in which the seek was attempted.
+   */
+  public final Timeline timeline;
+  /**
+   * The index of the window being seeked to.
+   */
+  public final int windowIndex;
+  /**
+   * The seek position in the specified window.
+   */
+  public final long positionMs;
+
+  /**
+   * @param timeline The {@link Timeline} in which the seek was attempted.
+   * @param windowIndex The index of the window being seeked to.
+   * @param positionMs The seek position in the specified window.
+   */
+  public IllegalSeekPositionException(Timeline timeline, int windowIndex, long positionMs) {
+    this.timeline = timeline;
+    this.windowIndex = windowIndex;
+    this.positionMs = positionMs;
+  }
+
+}

library/src/main/java/com/google/android/exoplayer2/Renderer.java

@@ -149,7 +149,13 @@ public interface Renderer extends ExoPlayerComponent {
    * This method may be called when the renderer is in the following states:
    * This method may be called when the renderer is in the following states:
    * {@link #STATE_ENABLED}, {@link #STATE_STARTED}.
    * {@link #STATE_ENABLED}, {@link #STATE_STARTED}.
    */
    */
-  void setCurrentStreamIsFinal();
+  void setCurrentStreamFinal();
+
+  /**
+   * Returns whether the current {@link SampleStream} will be the final one supplied before the
+   * renderer is next disabled or reset.
+   */
+  boolean isCurrentStreamFinal();
 
 
   /**
   /**
    * Throws an error that's preventing the renderer from reading from its {@link SampleStream}. Does
    * Throws an error that's preventing the renderer from reading from its {@link SampleStream}. Does