Add Acid3-based page cycler....

Add Acid3-based page cycler.

This page cycler test completes when all of Acid3's tests
have run.  This differs from previous page cyclers which
complete within 15ms of the page's load event firing.
Therefore, this page cycler typically takes much longer
per iteration.

Slight modifications to run better in a file:/non-http:
environment:
 - add doctypes to xml documents
 - rename svg.xml -> svg.svg
 - append '.xhtml' to xhtml.[123]

With these changes, we score between 99 and 100 out of
100 for Acid3 along with the linktest error.  (As of
~2009/06/19.)  Test completion on a release build on my
Windows XP desktop takes ~1250ms (version 2.0.172.31).
Test completion on a debug build on the same Windows
desktop takes ~4741ms.

I have not figured out why this Acid3's cat image doesn't
disappear.  This is the single remaining discrepancy
between my file:-based version and running Acid3 directly
from:

 http://acid3.acidtests.org/

I doubt the failure to hide the cat image impacts this
test in a way that introduces noticeable variance.

BUG=12357
TEST=Start 'chrome.exe --enable-file-cookies', browse to
acid3/start.html, run 5 iterations, verify tests
complete.  Run 10 iterations.  Manually extend page
cycler test and verify acid3 test is correctly invoked,
results are correctly sent back to test harness.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=19546

[Nicolas Sylvain, 2009-06-29 22:54:22]

LGTM