Pinch zoom is blocked on mobile when viewing AMP pages

[mraccess77]

People with low vision use the pinch zoom feature in mobile browsers such as Safari to enlarge text. When you view an AMP page through the viewer such as after performing a search on iOS the page appears in an iFrame and pinch zoom seems to be disabled. Attempts to adjust font size in Safari for iOS through the reader features mean that text is then cutoff the edge.

Users should be able to pinch zoom into content or use features in mobile browsers to resize text.