It seems that the viewport meta tag with user-scalable set to yes and no maximum-scale attribute is not allowed to pinch zoom in Chrome on Android anymore. It works fine in iPhone/safari and used to work on Android but did something change recently? Is there another attribute that is required now?
<meta name="viewport" content="width=device-width, initial-scale=1">
and
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=yes">
both of these are being ignored by Chrome now, and the page cannot zoom in or out.