[NaCL SDK] nacl_io: add <sys/poll.h>

There are a few headers that are not included in newlib
and/or win32.  <poll.h> is one of them but <sys/poll.h>
was not.  Some code (specifically civetweb) expected
<sys/poll.h> to exist so this change adds it and makes
poll.h simply include it.

R=binji@chromium.org

Review URL: https://codereview.chromium.org/42343002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231022 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231022
Define SpeculativeRestoreTargetStatus metric.

This metric tracks memory status (loaded vs needs restore) of tabs targeted
with speculative tab restore.

BUG=311216

Review URL: https://codereview.chromium.org/40283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231023 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231023