mkvmuxer: Add codec id constant for VP10.

This was added in the libvpx's snapshot here:
https://chromium-review.googlesource.com/#/c/293861

Change-Id: I58b9635c62535ecdb0dff14dc294466262590861

mkvmuxer.cpp

@@ -1045,6 +1045,7 @@ const char Tracks::kOpusCodecId[] = "A_OPUS";
 const char Tracks::kVorbisCodecId[] = "A_VORBIS";
 const char Tracks::kVp8CodecId[] = "V_VP8";
 const char Tracks::kVp9CodecId[] = "V_VP9";
+const char Tracks::kVp10CodecId[] = "V_VP10";
 
 Tracks::Tracks() : track_entries_(NULL), track_entries_size_(0) {}
 

mkvmuxer.hpp

@@ -528,11 +528,12 @@ class Tracks {
  public:
   // Audio and video type defined by the Matroska specs.
   enum { kVideo = 0x1, kAudio = 0x2 };
-  // Opus, Vorbis, VP8, and VP9 codec ids defined by the Matroska specs.
+
   static const char kOpusCodecId[];
   static const char kVorbisCodecId[];
   static const char kVp8CodecId[];
   static const char kVp9CodecId[];
+  static const char kVp10CodecId[];
 
   Tracks();
   ~Tracks();