Add end-to-end decryption test with vectors

Added a test_mode flag to the libwvdrmengine plugin
to support verifying decryption results.

Change-Id: I9edbd6279d54fc495b5bbad8273c179106cad474

libwvdrmengine/mediacrypto/include/WVCryptoPlugin.h

@@ -29,7 +29,8 @@ class WVCryptoPlugin : public android::CryptoPlugin {
   DISALLOW_EVIL_CONSTRUCTORS(WVCryptoPlugin);
 
   wvcdm::WvContentDecryptionModule* const mCDM;
-  const wvcdm::CdmSessionId mSessionId;
+  wvcdm::CdmSessionId mSessionId;
+  bool mTestMode;
 };
 
 } // namespace wvdrm