Fix cenc mode support and add support for the .mp4a extension.

Also add encrypted HLS internal sample streams.

Issue:#1661

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=175577648

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/DefaultHlsExtractorFactory.java

@@ -43,6 +43,7 @@ public final class DefaultHlsExtractorFactory implements HlsExtractorFactory {
   public static final String MP3_FILE_EXTENSION = ".mp3";
   public static final String MP4_FILE_EXTENSION = ".mp4";
   public static final String M4_FILE_EXTENSION_PREFIX = ".m4";
+  public static final String MP4_FILE_EXTENSION_PREFIX = ".mp4";
   public static final String VTT_FILE_EXTENSION = ".vtt";
   public static final String WEBVTT_FILE_EXTENSION = ".webvtt";
 
@@ -71,7 +72,8 @@ public Pair<Extractor, Boolean> createExtractor(Extractor previousExtractor, Uri
       // Only reuse TS and fMP4 extractors.
       extractor = previousExtractor;
     } else if (lastPathSegment.endsWith(MP4_FILE_EXTENSION)
-        || lastPathSegment.startsWith(M4_FILE_EXTENSION_PREFIX, lastPathSegment.length() - 4)) {
+        || lastPathSegment.startsWith(M4_FILE_EXTENSION_PREFIX, lastPathSegment.length() - 4)
+        || lastPathSegment.startsWith(MP4_FILE_EXTENSION_PREFIX, lastPathSegment.length() - 5)) {
       extractor = new FragmentedMp4Extractor(0, timestampAdjuster, null, drmInitData,
           muxedCaptionFormats != null ? muxedCaptionFormats : Collections.<Format>emptyList());
     } else {

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/playlist/HlsPlaylistParser.java

@@ -109,7 +109,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
   private static final Pattern REGEX_ATTR_BYTERANGE =
       Pattern.compile("BYTERANGE=\"(\\d+(?:@\\d+)?)\\b\"");
   private static final Pattern REGEX_METHOD = Pattern.compile("METHOD=(" + METHOD_NONE + "|"
-      + METHOD_AES_128 + "|" + METHOD_SAMPLE_AES + ")");
+      + METHOD_AES_128 + "|" + METHOD_SAMPLE_AES + "|" + METHOD_SAMPLE_AES_CENC + ")");
   private static final Pattern REGEX_KEYFORMAT = Pattern.compile("KEYFORMAT=\"(.+?)\"");
   private static final Pattern REGEX_URI = Pattern.compile("URI=\"(.+?)\"");
   private static final Pattern REGEX_IV = Pattern.compile("IV=([^,.*]+)");
@@ -391,7 +391,7 @@ private static HlsMediaPlaylist parseMediaPlaylist(LineIterator iterator, String
         segmentDurationUs =
             (long) (parseDoubleAttr(line, REGEX_MEDIA_DURATION) * C.MICROS_PER_SECOND);
       } else if (line.startsWith(TAG_KEY)) {
-        String method = parseStringAttr(line, REGEX_METHOD);
+        String method = parseOptionalStringAttr(line, REGEX_METHOD);
         String keyFormat = parseOptionalStringAttr(line, REGEX_KEYFORMAT);
         encryptionKeyUri = null;
         encryptionIV = null;
@@ -405,7 +405,7 @@ private static HlsMediaPlaylist parseMediaPlaylist(LineIterator iterator, String
               // Do nothing. Samples are encrypted using an identity key, but this is not supported.
               // Hopefully, a traditional DRM alternative is also provided.
             }
-          } else {
+          } else if (method != null) {
             SchemeData schemeData = parseWidevineSchemeData(line, keyFormat);
             if (schemeData != null) {
               drmInitData = new DrmInitData(METHOD_SAMPLE_AES_CENC.equals(method)