mkvparser: minor SeekHead::Entry clean up.

- Store actual element ID in SeekHead::Entry id field (instead
  of a decoded EBML int, which is completely _wrong_).
- Add a SeekHead::Entry constructor so we get initialized values
  in SeekHead::Entry's when parsing an Entry fails.

Change-Id: I152fae54628cb84918917139dba0cd0b42a44a57

mkvparser/mkvparser.cc

@@ -1476,6 +1476,8 @@ long Segment::Load() {
   }
 }
 
+SeekHead::Entry::Entry() : id(0), pos(0), element_start(0), element_size(0) {}
+
 SeekHead::SeekHead(Segment* pSegment, long long start, long long size_,
                    long long element_start, long long element_size)
     : m_pSegment(pSegment),
@@ -1767,18 +1769,7 @@ bool SeekHead::ParseEntry(IMkvReader* pReader, long long start, long long size_,
   if ((pos + seekIdSize) > stop)
     return false;
 
-  // Note that the SeekId payload really is serialized
-  // as a "Matroska integer", not as a plain binary value.
-  // In fact, Matroska requires that ID values in the
-  // stream exactly match the binary representation as listed
-  // in the Matroska specification.
-  //
-  // This parser is more liberal, and permits IDs to have
-  // any width.  (This could make the representation in the stream
-  // different from what's in the spec, but it doesn't matter here,
-  // since we always normalize "Matroska integer" values.)
-
-  pEntry->id = ReadUInt(pReader, pos, len);  // payload
+  pEntry->id = ReadID(pReader, pos, len);  // payload
 
   if (pEntry->id <= 0)
     return false;

mkvparser/mkvparser.h

@@ -844,6 +844,8 @@ class SeekHead {
   long Parse();
 
   struct Entry {
+    Entry();
+
     // the SeekHead entry payload
     long long id;
     long long pos;

testing/test_util.cc

@@ -73,10 +73,7 @@ bool HasCuePoints(const mkvparser::Segment* segment,
   std::int64_t offset = 0;
   for (int i = 0; i < seek_head->GetCount(); ++i) {
     const SeekHead::Entry* const entry = seek_head->GetEntry(i);
-    // TODO(tomfinegan): Cues ID is really 0x1C53BB6B, aka kMkvCues, but
-    // mkvparser reads IDs as EBML unsigned ints in some cases, yielding magic
-    // numbers like the following. Investigate fixing this behavior.
-    if (entry->id == 0xC53BB6B) {  // Cues ID as stored in Entry class.
+    if (entry->id == libwebm::kMkvCues) {
       offset = entry->pos;
     }
   }