Pepper: Small cleanup in trusted plugin.

This reduces the lifetime of ErrorInfo when passed to LoadNaClModule(), which
makes it easier to make LoadNaClModule() asynchronous in the future.

This is split off from the prototype change I've got to move module loading to
Chromium IPC from SRPC.

BUG=333950
R=dmichael@chromium.org

Review URL: https://codereview.chromium.org/151223003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248792 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248792