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It's no longer necessary for the NaCl side to define and refer to the
NaClFileToken struct.

So we can change the Chromium side to define NaClFileToken, instead of
using the definition from nacl_file_info.h.  This will let us remove
nacl_file_info.h from the NaCl side.

We copy the comment from nacl_file_info.h.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=4073
TEST=build

Review URL: https://codereview.chromium.org/903333002

Cr-Commit-Position: refs/heads/master@{#315317}