This doesn't really answer your question about a Google Chrome bug, but this is my recommendation for your particular situation:
I would use CSS
instead of setting the page up with JavaScript:
EXAMPLE
Example on JSBin
HTML
<div id="received">27 Emails received since Wed, 06 Jan 2010 05:00:05</div>
<div id="sent">10 Emails sent since Wed, 06 Jan 2010 05:00:05</div>
CSS:
html, body { height: 100%; width: 100%; position: relative; margin: 0; padding: 0 }
#received, #sent { position: absolute; left: 0; width: 100%; }
#received { top: 0; bottom: 200px; background-color: #ff0000; }
#sent { bottom: 0; height: 200px; background-color: #0000ff; }
UPDATE
You could still play with the split ratio using JavaScript, but it would always fill the screen, even if the calculations are 2 or 3 pixels off from what you ideally wanted:
JS
var received = document.getElementById('received'),
sent = document.getElementById('sent');
// Be sure to set 'sent' height to whatever you set 'received' bottom to:
received.style.bottom = "300px";
sent.style.height = "300px";
// You should also be able to use percentages:
received.style.bottom = "30%"; // Received will occupy 70%
sent.style.height = "30%"; // Sent will occupy 30%