ThreadRestrictions: disallow blocking IO on the UI thread

This patch sets the "disallow IO" flag after the UI thread has
started, and then whitelists in the many places where we're
accidentally doing IO from the UI thread.  (I've filed bugs
on all of those cases.)

BUG=59847,60630,60641,60211,60634,60643,24163,60825

Review URL: http://codereview.chromium.org/4146004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@63986 0039d316-1c4b-4281-b951-d872f2087c98
9 files changed