[NaCl SDK] Run browser tests with --disable-component-update

The PNaCl installer is more aggressive right now and
checks for updates on each pexe load. Disable this behavior
to test the copy of PNaCl that is already built instead of
downloading the "official" one.

A separate CL will make this less aggressive, but it's not
clear if that will be flexible enough to detect pre-built
copies of PNaCl vs official copies. E.g., if it's just based
on min_version vs cur_version of official copies then it
will ignore the pre-built copies.

Re-enable nacl_io_test. It was timing out before because
of the installation delay. The installation delay is less
now due to component updater timer tweaks (2 seconds),
but having --disable-component-update reduces that to 0.

BUG=315253
NOTRY=true
(sdk only)

Review URL: https://codereview.chromium.org/70633002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234638 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234638