Revert 116816 - Hook up the SequencedWorkerPool to the browser thread.

Revert 116816 - Hook up the SequencedWorkerPool to the browser thread.

This does some refactoring of the static data in the browser thread so we only have one global object instead of a bunch fo separate arrays.

It also hooks up the visited link master's I/O to use this new system as a proof of concept.
Review URL: http://codereview.chromium.org/9065009

TBR=brettw@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=116817