Change mojo enums to be scoped enums in the generated C++ bindings.

media/mojo/interfaces/decryptor.mojom

Index: media/mojo/interfaces/decryptor.mojom
diff --git a/media/mojo/interfaces/decryptor.mojom b/media/mojo/interfaces/decryptor.mojom
index 64e1b63168674b5e27c3587f69c1966ba43c29f7..d063e6b7a1a9aff87398b81f5828d6fac2223540 100644
--- a/media/mojo/interfaces/decryptor.mojom
+++ b/media/mojo/interfaces/decryptor.mojom
@@ -16,7 +16,8 @@ interface Decryptor {
     SUCCESS,  // Successfully completed. Decrypted buffer ready.
     NO_KEY,  // No key is available to decrypt.
     NEED_MORE_DATA,  // Decoder needs more data to produce an output.
-    ERROR  // Key is available but an error occurred during decryption.
+    // Key is available but an error occurred during decryption.
+    DECRYPTION_ERROR
   };
 
   // Pass the two data pipes used to transfer DecoderBuffer contents to and