tiny fonts in Chrome rendered web content (not the browser's user interface)

I am running Ubuntu 16.04 64bit.

Chrome (54.0.2840.100 64-bit) fonts appear very small in some places. I am referring to the rendered web content, not the browser's user interface.

The following is the way Chrome renders the new email "window" in Gmail. Observe how tiny "To" and "Subject" appear in relation to "New Message".

In contrast, Firefox renders the same "window" with more reasonable fonts (observe how "To" and "Subject" appear to be closer in size to "New Message"):