Clean up error message in schema-based policy validation

Make the error message a little bit more readable.

Old example:
"Dropping policy Undeclared for aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa because it's not valid: The schema is invalid. at "

Example after the change:
"Dropping policy Undeclared of component aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa due to error at root: The schema is invalid."

BUG=none
TEST=none

Review-Url: https://codereview.chromium.org/2541793006
Cr-Commit-Position: refs/heads/master@{#435921}


CrOS-Libchrome-Original-Commit: 4372393deb7e34ba940a3687910df7f7ff128e53
1 file changed
tree: bc9d813beff03556386cb44c17b054f6937cff0d
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/