Android WebView: use IO thread for cookie manager.

Instead of posting tasks to the FILE thread, use the IO thread to match
the rest of Chromium (which normally only calls CookieMonster on the IO
thread). This is a workaround for a possible thread safety issue in
CookieMonster (see, but it's fine to change
this permanently as the original choice of the FILE thread was not

Bug: 11265317
Change-Id: I0f54d9ce9408d17312e312d4b919b542dcac4828
1 file changed