Move viewport unit resolution to style recalc time

LayoutTests/fast/css/computed-offset-with-zoom.html

Index: LayoutTests/fast/css/computed-offset-with-zoom.html
diff --git a/LayoutTests/fast/css/computed-offset-with-zoom.html b/LayoutTests/fast/css/computed-offset-with-zoom.html
index 921bc1906cc1ba93ec4cb4d7cae06bedd31f7b54..27d8be4f39b3359f272f64b146caec1a4a90e1dc 100644
--- a/LayoutTests/fast/css/computed-offset-with-zoom.html
+++ b/LayoutTests/fast/css/computed-offset-with-zoom.html
@@ -51,8 +51,8 @@
             function test(zoomLevel)
             {
                     document.body.style.zoom = zoomLevel;
-                    var windowWidth = "'" + (window.innerWidth / 10 / zoomLevel) + "px'";
-                    var windowHeight = "'" + (window.innerHeight / 10 / zoomLevel) + "px'";
+                    var windowWidth = "'" + (window.innerWidth / 10) + "px'";

[kenneth.r.christiansen, 2013/12/16 10:08:19]

So these were just bugs? Do we have tests testing with page zoom (aka browser
zoom) which affects the initial viewport?

[Timothy Loh, 2013/12/17 05:09:15]

Err, turns out the test is actually correct already (or at least firefox behaves
the same way when zooming with viewport units). I've reverted the test change
and updated computeLength to be more correct.

Note I'm not fixing here the issue from
http://lists.w3.org/Archives/Public/www-style/2012Aug/0568.html, which is a
separate issue (font-size in viewport units get zoom applied twice instead of
once). I'll have a look at that separately later.

[Timothy Loh, 2013/12/17 22:58:00]

Actually I thought about it a bit more and changed my mind here. I've settled on
having browser zoom not affect the (visual) size of viewport units, but
style.zoom affecting it. The browser zoom part here is consistent with other
browsers.

The zoom CSS property is non-standard (Firefox doesn't implement it), but having
this affect the visual size is a bit more consistent. In particular, CSS zoom
currently resizes all other <length>s, so this will stop being an exception.
This also moves zoom closer to transform: scale(..), which would also (visually)
resize objects with viewport-unit dimensions.

Fixing this turned out to be pretty easy, and the issue linked above also gets
fixed. I'll add a test shortly.

+                    var windowHeight = "'" + (window.innerHeight / 10) + "px'";
                     
                     shouldBe("window.getComputedStyle(fixedElement).top", "'100px'");
                     shouldBe("window.getComputedStyle(fixedElement).right", "'100px'");