Add support for encrypted WebM files as defined in the RFC.

media/webm/webm_constants.h

Index: media/webm/webm_constants.h
diff --git a/media/webm/webm_constants.h b/media/webm/webm_constants.h
index b6ba0a21c49f8a850e9f76440ea89aacec5c021a..93041b29c67c6067f468e032b5fddf0a9601be6f 100644
--- a/media/webm/webm_constants.h
+++ b/media/webm/webm_constants.h
@@ -12,6 +12,7 @@ namespace media {
 // WebM element IDs.
 // This is a subset of the IDs in the Matroska spec.
 // http://www.matroska.org/technical/specs/index.html
+const int kWebMIdAESSettingsCipherMode = 0x47E8;
 const int kWebMIdAspectRatioType = 0x54B3;
 const int kWebMIdAttachedFile = 0x61A7;
 const int kWebMIdAttachmentLink = 0x7446;
@@ -62,6 +63,7 @@ const int kWebMIdColorSpace = 0x2EB524;
 const int kWebMIdContentCompAlgo = 0x4254;
 const int kWebMIdContentCompression = 0x5034;
 const int kWebMIdContentCompSettings = 0x4255;
+const int kWebMIdContentEncAESSettings = 0x47E7;
 const int kWebMIdContentEncAlgo = 0x47E1;
 const int kWebMIdContentEncKeyID = 0x47E2;
 const int kWebMIdContentEncoding = 0x6240;
@@ -197,6 +199,11 @@ const int64 kWebMUnknownSize = GG_LONGLONG(0x00FFFFFFFFFFFFFF);
 
 const uint8 kWebMFlagKeyframe = 0x80;
 
+// The size is from the WebM encrypted specification. Current encrypted WebM
+// request for comments specification is here
+// http://wiki.webmproject.org/encryption/webm-encryption-rfc
+const int kWebMHmacSize = 12;
+
 }  // namespace media
 
 #endif  // MEDIA_WEBM_WEBM_CONSTANTS_H_