Set file tokens for NaCl main nexe if available to enable validation caching.
Also enable mmap'ing the main nexe, which may help a bit
in subsequent runs as well (first run the validator needs
page in all of the text anyway).
pnacl-llc.nexe, etc will be handled separately:
https://codereview.chromium.org/
224803002/
TEST=NaClBrowserTestVcacheExtension.ValidationCacheOfMainNexe
BUG=https://code.google.com/p/nativeclient/issues/detail?id=3421
Review URL: https://codereview.chromium.org/
263683002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272429 0039d316-1c4b-4281-b951-d872f2087c98