Account for flags and version when parsing an EMSG box.

Added version and flag bytes to the test code.
Added the code to skip version and flag bytes when
parsing an EMSG box.

Closes #259.

Change-Id: Iac94785f747ec6ffb640c5b4f803e68e0c7b27cb

lib/dash/dash_parser.js

@@ -1297,6 +1297,8 @@ shaka.dash.DashParser.prototype.emsgResponseFilter_ = function(type, response) {
     if (boxSize != shaka.util.Mp4Parser.BOX_NOT_FOUND) {
       var start = reader.getPosition() - 8;
       var end = start + boxSize;
+      // skip version and flags
+      reader.skip(4);
       var scheme_id = reader.readTerminatedString();
       // scheme_id of "urn:mpeg:dash:event:2012" means it's
       // time to update the manifest

test/dash/dash_parser_manifest_unit.js

@@ -764,20 +764,20 @@ describe('DashParser.Manifest', function() {
     ]);
 
     var emsgUpdate = new Uint8Array([
-      0, 0, 0, 48, 101, 109, 115, 103,
-      117, 114, 110, 58, 109, 112, 101,
-      103, 58, 100, 97, 115, 104, 58,
-      101, 118, 101, 110, 116, 58, 50,
-      48, 49, 50, 0, 0, 0, 49, 0, 0, 0,
-      8, 0, 0, 255, 255, 116, 101, 115,
-      116
+      0, 0, 0, 52, 101, 109, 115, 103,
+      0, 0, 0, 0, 117, 114, 110, 58,
+      109, 112, 101, 103, 58, 100, 97,
+      115, 104, 58, 101, 118, 101, 110,
+      116, 58, 50, 48, 49, 50, 0, 0, 0,
+      49, 0, 0, 0, 8, 0, 0, 255, 255, 116,
+      101, 115, 116
     ]);
 
     var emsgCustom = new Uint8Array([
-      0, 0, 0, 55, 101, 109, 115, 103,
-      102, 111, 111, 58, 98, 97, 114,
-      58, 99, 117, 115, 116, 111, 109,
-      100, 97, 116, 97, 115, 99, 104,
+      0, 0, 0, 59, 101, 109, 115, 103,
+      0, 0, 0, 0, 102, 111, 111, 58, 98,
+      97, 114, 58, 99, 117, 115, 116, 111,
+      109, 100, 97, 116, 97, 115, 99, 104,
       101, 109, 101, 0, 49, 0, 0, 0, 0,
       1, 0, 0, 0, 8, 0, 0, 255, 255, 0,
       0, 0, 1, 116, 101, 115, 116