message: fix handling of volatile proguard keyword
  Summary: It seems our proguard parser wasn't working on `volatile` fields.
diff: @@ -322,6 +322,8 @@ DexAccessFlags process_access_modifier(token type, bool* is_access_flag) {
  return ACC_ENUM;
  case token::staticToken:
  return ACC_STATIC;
  + case token::volatileToken:
  + return ACC_VOLATILE;
  case token::native:
  return ACC_NATIVE;
  case token::protectedToken:
  @@ -345,6 +347,7 @@ bool is_negation_or_class_access_modifier(token type) {
  case token::synthetic:
  case token::native:
  case token::staticToken:
  + case token::volatileToken:
  case token::transient:
  case token::annotation:
  return true;
  