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

media/base/decrypt_config.cc

Index: media/base/decrypt_config.cc
diff --git a/media/base/decrypt_config.cc b/media/base/decrypt_config.cc
index 9ae5f195e5d4cfab2be9a45108b23d329d2732e4..d5bc88bf03e789906a8a198a7e097ebb32a90ef0 100644
--- a/media/base/decrypt_config.cc
+++ b/media/base/decrypt_config.cc
@@ -8,9 +8,16 @@
 
 namespace media {
 
-DecryptConfig::DecryptConfig(const uint8* key_id, int key_id_size)
-    : key_id_size_(key_id_size) {
+DecryptConfig::DecryptConfig(const uint8* hmac, int hmac_size,
+                             uint64 iv,
+                             const uint8* key_id, int key_id_size)
+    :  hmac_size_(hmac_size),
+       iv_(iv),
+       key_id_size_(key_id_size) {
+  CHECK_GT(hmac_size, 0);
   CHECK_GT(key_id_size, 0);
+  hmac_.reset(new uint8[hmac_size]);
+  memcpy(hmac_.get(), hmac, hmac_size);
   key_id_.reset(new uint8[key_id_size]);
   memcpy(key_id_.get(), key_id, key_id_size);
 }