Only content/ now has the ability to create BrowserThread objects,
with the exception that tests can create the
content::TestBrowserThread subclass, and (temporarily) code in chrome/
can create the DeprecatedBrowserThread subclass.
A follow-up change will make content/ take care of its own thread
creation, remove DeprecatedBrowserThread, and move all state and
non-trivial constructors from BrowserThread down to BrowserThreadImpl.
Also moved BrowserProcessSubThread into content/ namespace. As part
of follow-up cleanup, chrome/ will stop using this class.
BUG=98716
TEST=existing
Review URL: http://codereview.chromium.org/8392042
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@107718 0039d316-1c4b-4281-b951-d872f2087c98
c38831a108