Export to data-uri no longer works on Chrome

[juliandescottes]

Steps to reproduce:

• use Chrome 60 or newer
• draw something
• open export panel
• go to PNG tab
• click on To data-uri

Expected results:

• opens a new browser tab with your image

Actual results:

• opens a blank page

[juliandescottes]

Recently Chrome removed the possibility to navigate to data-uris:

• intent to remove: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/GbVcuwg_QjM
• chromium bug: https://bugs.chromium.org/p/chromium/issues/detail?id=594215

The suggested workaround for now seems to be to use an iframe: https://bugs.chromium.org/p/chromium/issues/detail?id=594215#c64

Note that this will also be implemented in Firefox starting with FF56: https://bugzilla.mozilla.org/show_bug.cgi?id=1331351