Remove the checksum/HMAC code from the decryptor.

ppapi/api/private/pp_content_decryptor.idl

Index: ppapi/api/private/pp_content_decryptor.idl
diff --git a/ppapi/api/private/pp_content_decryptor.idl b/ppapi/api/private/pp_content_decryptor.idl
index 099cfe9f6d8669eb7daccfd06ef597bf43e8ae3c..14d9c1c596ff3fb793fef88a6563ae8671ad7730 100644
--- a/ppapi/api/private/pp_content_decryptor.idl
+++ b/ppapi/api/private/pp_content_decryptor.idl
@@ -76,7 +76,7 @@ struct PP_DecryptSubsampleDescription {
  * The <code>PP_EncryptedBlockInfo</code> struct contains all the information
  * needed to decrypt an encrypted block.
  */
-[assert_size(256)]
+[assert_size(240)]
 struct PP_EncryptedBlockInfo {
   /**
    * Information needed by the client to track the block to be decrypted.
@@ -107,12 +107,6 @@ struct PP_EncryptedBlockInfo {
   uint32_t iv_size;
 
   /**
-   * Checksum of the block to be decrypted.
-   */
-  uint8_t[12] checksum;
-  uint32_t checksum_size;
-
-  /**
    * Subsample information of the block to be decrypted.
    */
   PP_DecryptSubsampleDescription[16] subsamples;