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

media/webm/webm_cluster_parser.cc

Index: media/webm/webm_cluster_parser.cc
diff --git a/media/webm/webm_cluster_parser.cc b/media/webm/webm_cluster_parser.cc
index 5b18c56e106a520df5e801b1a899a341a1ea8a7e..43149833c7c9382c3dd1d7a939a6eb310e18893e 100644
--- a/media/webm/webm_cluster_parser.cc
+++ b/media/webm/webm_cluster_parser.cc
@@ -5,6 +5,7 @@
 #include "media/webm/webm_cluster_parser.h"
 
 #include "base/logging.h"
+#include "base/sys_byteorder.h"
 #include "media/base/data_buffer.h"
 #include "media/base/decrypt_config.h"
 #include "media/webm/webm_constants.h"
@@ -187,15 +188,33 @@ bool WebMClusterParser::OnBlock(int track_num, int timecode,
   base::TimeDelta timestamp = base::TimeDelta::FromMicroseconds(
       (cluster_timecode_ + timecode) * timecode_multiplier_);
 
+  // Every encrypted Block has an HMAC and IV prepended to it. Current WebM
+  // encrypted request for comments specification is here
+  // http://wiki.webmproject.org/encryption/webm-encryption-rfc
+  bool encrypted = track_num == video_.track_num() &&
+                         video_encryption_key_id_.get();
+  // If encrypted skip past the HMAC.
+  int data_offset = (encrypted) ? kWebMIntegrityCheckSize : 0;
+
   // The first bit of the flags is set when the block contains only keyframes.
   // http://www.matroska.org/technical/specs/index.html
   bool is_keyframe = (flags & 0x80) != 0;
   scoped_refptr<StreamParserBuffer> buffer =
-      StreamParserBuffer::CopyFrom(data, size, is_keyframe);
-
-  if (track_num == video_.track_num() && video_encryption_key_id_.get()) {
+      StreamParserBuffer::CopyFrom(data + data_offset,
+                                   size - data_offset,
+                                   is_keyframe);
+
+  if (encrypted) {
+    uint64 network_iv;
+    memcpy(&network_iv,
+           data + kWebMIntegrityCheckSize,
+           sizeof(network_iv));
+    const uint64 iv = base::NetToHost64(network_iv);
     buffer->SetDecryptConfig(scoped_ptr<DecryptConfig>(new DecryptConfig(
-        video_encryption_key_id_.get(), video_encryption_key_id_size_)));
+        data, kWebMIntegrityCheckSize,
+        reinterpret_cast<const uint8*>(&iv), sizeof(iv),
+        video_encryption_key_id_.get(), video_encryption_key_id_size_,
+        sizeof(iv))));
   }
 
   buffer->SetTimestamp(timestamp);