Don't use ParsableBitArray to parse TS packet headers

Really low hanging fruit optimization for TS extraction.

ParsableBitArray is quite expensive. In particular readBits
contains at least 2 if blocks and a for loop, and was being
called 5 times per 188 byte packet (4 times via readBit). A
separate change will follow that optimizes readBit, but for
this particular case there's no real value to using a
ParsableBitArray anyway; use of ParsableBitArray IMO only
really becomes useful when you need to parse a bitstream more
than 4 bytes long, or where parsing the bitstream requires
some control flow (if/for) to parse.

There are probably other places where we're using
ParsableBitArray over-zealously. I'll roll that into a
tracking bug for looking in more detail at all extractors.

Issue: #3040

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=161650940

library/core/src/main/java/com/google/android/exoplayer2/extractor/ts/TsExtractor.java

@@ -111,7 +111,6 @@ public final class TsExtractor implements Extractor {
   @Mode private final int mode;
   private final List<TimestampAdjuster> timestampAdjusters;
   private final ParsableByteArray tsPacketBuffer;
-  private final ParsableBitArray tsScratch;
   private final SparseIntArray continuityCounters;
   private final TsPayloadReader.Factory payloadReaderFactory;
   private final SparseArray<TsPayloadReader> tsPayloadReaders; // Indexed by pid
@@ -164,7 +163,6 @@ public final class TsExtractor implements Extractor {
       timestampAdjusters.add(timestampAdjuster);
     }
     tsPacketBuffer = new ParsableByteArray(BUFFER_SIZE);
-    tsScratch = new ParsableBitArray(new byte[3]);
     trackIds = new SparseBooleanArray();
     tsPayloadReaders = new SparseArray<>();
     continuityCounters = new SparseIntArray();
@@ -250,24 +248,23 @@ public final class TsExtractor implements Extractor {
       return RESULT_CONTINUE;
     }
 
-    tsPacketBuffer.skipBytes(1);
-    tsPacketBuffer.readBytes(tsScratch, 3);
-    if (tsScratch.readBit()) { // transport_error_indicator
+    int tsPacketHeader = tsPacketBuffer.readInt();
+    if ((tsPacketHeader & 0x800000) != 0) { // transport_error_indicator
       // There are uncorrectable errors in this packet.
       tsPacketBuffer.setPosition(endOfPacket);
       return RESULT_CONTINUE;
     }
-    boolean payloadUnitStartIndicator = tsScratch.readBit();
-    tsScratch.skipBits(1); // transport_priority
-    int pid = tsScratch.readBits(13);
-    tsScratch.skipBits(2); // transport_scrambling_control
-    boolean adaptationFieldExists = tsScratch.readBit();
-    boolean payloadExists = tsScratch.readBit();
+    boolean payloadUnitStartIndicator = (tsPacketHeader & 0x400000) != 0;
+    // Ignoring transport_priority (tsPacketHeader & 0x200000)
+    int pid = (tsPacketHeader & 0x1FFF00) >> 8;
+    // Ignoring transport_scrambling_control (tsPacketHeader & 0xC0)
+    boolean adaptationFieldExists = (tsPacketHeader & 0x20) != 0;
+    boolean payloadExists = (tsPacketHeader & 0x10) != 0;
 
     // Discontinuity check.
     boolean discontinuityFound = false;
-    int continuityCounter = tsScratch.readBits(4);
     if (mode != MODE_HLS) {
+      int continuityCounter = tsPacketHeader & 0xF;
       int previousCounter = continuityCounters.get(pid, continuityCounter - 1);
       continuityCounters.put(pid, continuityCounter);
       if (previousCounter == continuityCounter) {
@@ -276,7 +273,7 @@ public final class TsExtractor implements Extractor {
           tsPacketBuffer.setPosition(endOfPacket);
           return RESULT_CONTINUE;
         }
-      } else if (continuityCounter != (previousCounter + 1) % 16) {
+      } else if (continuityCounter != ((previousCounter + 1) & 0xF)) {
         discontinuityFound = true;
       }
     }
@@ -296,7 +293,6 @@ public final class TsExtractor implements Extractor {
         }
         tsPacketBuffer.setLimit(endOfPacket);
         payloadReader.consume(tsPacketBuffer, payloadUnitStartIndicator);
-        Assertions.checkState(tsPacketBuffer.getPosition() <= endOfPacket);
         tsPacketBuffer.setLimit(limit);
       }
     }