libmkv: constify codec_id.

This lets the caller pass a string literal for the codec id.

From https://bugzilla.mozilla.org/show_bug.cgi?id=966044

Change-Id: I345bd7a5943f0c33b3fb368d4280100ac5038a3d

third_party/libmkv/WebMElement.c

@@ -52,8 +52,9 @@ static UInt64 generateTrackID(unsigned int trackNumber) {
   return rval;
 }
 
-void writeVideoTrack(EbmlGlobal *glob, unsigned int trackNumber, int flagLacing,
-                     char *codecId, unsigned int pixelWidth, unsigned int pixelHeight,
+void writeVideoTrack(EbmlGlobal *glob, unsigned int trackNumber,
+                     int flagLacing, const char *codecId,
+                     unsigned int pixelWidth, unsigned int pixelHeight,
                      double frameRate) {
   EbmlLoc start;
   Ebml_StartSubElement(glob, &start, TrackEntry);
@@ -74,8 +75,9 @@ void writeVideoTrack(EbmlGlobal *glob, unsigned int trackNumber, int flagLacing,
   }
   Ebml_EndSubElement(glob, &start); // Track Entry
 }
-void writeAudioTrack(EbmlGlobal *glob, unsigned int trackNumber, int flagLacing,
-                     char *codecId, double samplingFrequency, unsigned int channels,
+void writeAudioTrack(EbmlGlobal *glob, unsigned int trackNumber,
+                     int flagLacing, const char *codecId,
+                     double samplingFrequency, unsigned int channels,
                      unsigned char *private, unsigned long privateSize) {
   EbmlLoc start;
   Ebml_StartSubElement(glob, &start, TrackEntry);

third_party/libmkv/WebMElement.h

@@ -12,19 +12,21 @@
 
 // these are helper functions
 void writeHeader(EbmlGlobal *ebml);
-void writeSegmentInformation(EbmlGlobal *ebml, EbmlLoc *startInfo, unsigned long timeCodeScale, double duration);
+void writeSegmentInformation(EbmlGlobal *ebml, EbmlLoc *startInfo,
+                             unsigned long timeCodeScale, double duration);
 // this function is a helper only, it assumes a lot of defaults
-void writeVideoTrack(EbmlGlobal *ebml, unsigned int trackNumber, int flagLacing,
-                     char *codecId, unsigned int pixelWidth, unsigned int pixelHeight,
+void writeVideoTrack(EbmlGlobal *ebml, unsigned int trackNumber,
+                     int flagLacing, const char *codecId,
+                     unsigned int pixelWidth, unsigned int pixelHeight,
                      double frameRate);
-void writeAudioTrack(EbmlGlobal *glob, unsigned int trackNumber, int flagLacing,
-                     char *codecId, double samplingFrequency, unsigned int channels,
+void writeAudioTrack(EbmlGlobal *glob, unsigned int trackNumber,
+                     int flagLacing, const char *codecId,
+                     double samplingFrequency, unsigned int channels,
                      unsigned char *private, unsigned long privateSize);
 
-void writeSimpleBlock(EbmlGlobal *ebml, unsigned char trackNumber, short timeCode,
-                      int isKeyframe, unsigned char lacingFlag, int discardable,
+void writeSimpleBlock(EbmlGlobal *ebml, unsigned char trackNumber,
+                      short timeCode, int isKeyframe,
+                      unsigned char lacingFlag, int discardable,
                       unsigned char *data, unsigned long dataLength);
 
-
-
-#endif
\ No newline at end of file
+#endif