Off-shoot from bug 93862. Text Autosizing makes text bigger on the assumption that you'll be able to zoom out and see a wider area all at once (which will be legible due to the autosizing). However if the user is prevented from zooming out, for example with:
<meta name="viewport" content="width=980, minimum-scale=1, maximum-scale=1">
then the user won't be able to zoom out, and the increase in text size will be futile - indeed, it will make the text harder to read!.
The multiplier calculated in TextAutosizer::processBox should be capped to 1 / minPageScaleFactor, where minPageScaleFactor takes into account the viewport constraints, and any default constraints set by the browser.
Currently minPageScaleFactor isn't known to WebCore (despite being the viewport part of this being calculated in WebCore/dom/ViewportArguments.cpp), so the main prerequisite for this is for ports to plumb their minPageScaleFactors into WebCore.
Marking this bug Resolved WontFix because the TEXT_AUTOSIZING feature was removed in <https://trac.webkit.org/changeset/206119> (bug #162167). See bug 84186, comment 32 for more details.