Add support for a bext chunk *before* the fmt chunk in WAV files.

This can occur in some Broadcast Wave Format (BWF) files, such as those
produced by the Zoom H2n. See the included sample for an example.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120334117

library/src/main/java/com/google/android/exoplayer/extractor/wav/WavHeaderReader.java

@@ -52,8 +52,8 @@ import java.io.IOException;
     ParsableByteArray scratch = new ParsableByteArray(16);
 
     // Attempt to read the RIFF chunk.
-    ChunkHeader riffChunkHeader = ChunkHeader.peek(input, scratch);
-    if (riffChunkHeader.id != Util.getIntegerCodeForString("RIFF")) {
+    ChunkHeader chunkHeader = ChunkHeader.peek(input, scratch);
+    if (chunkHeader.id != Util.getIntegerCodeForString("RIFF")) {
       return null;
     }
 
@@ -65,13 +65,17 @@ import java.io.IOException;
       return null;
     }
 
-    // Attempt to read the format chunk.
-    ChunkHeader formatChunkHeader = ChunkHeader.peek(input, scratch);
-    if (formatChunkHeader.id != Util.getIntegerCodeForString("fmt ")) {
-      throw new ParserException(
-          "Second chunk in RIFF WAV should be format; got: " + formatChunkHeader.id);
+    // If a bext chunk is present, skip it. Otherwise we expect a format chunk.
+    chunkHeader = ChunkHeader.peek(input, scratch);
+    if (chunkHeader.id == Util.getIntegerCodeForString("bext")) {
+      input.advancePeekPosition((int) chunkHeader.size);
+      chunkHeader = ChunkHeader.peek(input, scratch);
+    }
+
+    if (chunkHeader.id != Util.getIntegerCodeForString("fmt ")) {
+      throw new ParserException("Expected format chunk; found: " + chunkHeader.id);
     }
-    Assertions.checkState(formatChunkHeader.size >= 16);
+    Assertions.checkState(chunkHeader.size >= 16);
 
     input.peekFully(scratch.data, 0, 16);
     scratch.setPosition(0);
@@ -101,7 +105,7 @@ import java.io.IOException;
     }
 
     // If present, skip extensionSize, validBitsPerSample, channelMask, subFormatGuid, ...
-    input.advancePeekPosition((int) formatChunkHeader.size - 16);
+    input.advancePeekPosition((int) chunkHeader.size - 16);
 
     return new WavHeader(
         numChannels, sampleRateHz, averageBytesPerSecond, blockAlignment, bitsPerSample);