Backed out changeset 21491130777e (bug 1848660) for causing assertion…

… failures on Casting.h. CLOSED TREE

dom/media/test/crashtests/crashtests.list

@@ -168,4 +168,3 @@ load 1840002.webm
 load 1845350.mp4
 load noextradata-8ch.html
 load invalidfmt.html
-load 1848660.html

dom/media/wave/WaveDemuxer.cpp

@@ -701,24 +701,21 @@ uint16_t FormatChunk::ExtraFormatInfoSize() const {
 }
 
 AudioConfig::ChannelLayout::ChannelMap FormatChunk::ChannelMap() const {
-  // Regular mapping if file doesn't have channel mapping info. Alternatively,
-  // if the chunk size doesn't have the field for the size of the extension
-  // data, return a regular mapping.
+  // Regular mapping if file doesn't have channel mapping info, of if the chunk
+  // size doesn't have the field for the size of the extension data.
   if (WaveFormat() != 0xFFFE || mRaw.Length() < 18) {
     return AudioConfig::ChannelLayout(Channels()).Map();
   }
   // The length of this chunk is at least 18, check if it's long enough to
   // hold the WAVE_FORMAT_EXTENSIBLE struct, that is 22 bytes. If not, fall
-  // back to a common mapping. The channel mapping is four bytes, starting at
-  // offset 18.
-  if (ExtraFormatInfoSize() < 22 || mRaw.Length() < 22) {
+  // back to a common mapping.
+  if (ExtraFormatInfoSize() < 22) {
     return AudioConfig::ChannelLayout(Channels()).Map();
   }
   // ChannelLayout::ChannelMap is by design bit-per-bit compatible with
   // WAVEFORMATEXTENSIBLE's dwChannelMask attribute, we can just cast here.
-  auto channelMap = static_cast<AudioConfig::ChannelLayout::ChannelMap>(
+  return static_cast<AudioConfig::ChannelLayout::ChannelMap>(
       mRaw[21] | mRaw[20] | mRaw[19] | mRaw[18]);
-  return channelMap;
 }
 
 // DataParser