Chrome Version: 55.0.2883.79, 54.0.2840.91
OS: iOS 10.2, 10.1.1, 10.0.2
Device models: ME276LL/A, MD793ZP/A, MD298J/A, ME818J/A

What steps will reproduce the problem?

Install the GMail app, and configure Chrome to launch the GMail app when a mailto: link is clicked
Visit a page with a mailto link that includes a _blank target attribute in the anchor, e.g.:
<a href="mailto:example@example.com" target="_blank">E-mail me!</a>

Example page is available at http://sites.google.com/a/woogie.systems/arbitrary
Links should be self-explanatory

What is the expected result?
GMail app opens

What happens instead?
iOS native mail app opens