Steps to reproduce the problem:
1. go offline
2. open Chrome
3. open any URL without offline page
4. click many times Download icon or many times click Download page later+refresh page

What is the expected behavior?
Page from URL is scheduled once for download

What went wrong?
Page from URL is scheduled many times for download

Did this work before? No 

Chrome version: 58  Channel: canary
OS Version: 6
Flash Version: 

https://codereview.chromium.org/2698593002/ - patch with fix