Revert of "Implement the inert attribute"

The revert did not apply cleanly, there were conflicts in:
- third_party/WebKit/Source/core/frame/UseCounter.h
- tools/metrics/histograms/enums.xml

Reason for revert:
The new added tests leak. See crbug.com/725815.

Original issue's description:
> Implement the inert attribute: https://github.com/WICG/inert#tldr
>
> https://discourse.wicg.io/t/inert-attribute/1838/
>
> BUG=692360
> Review-Url: https://codereview.chromium.org/2088453002
> Cr-Commit-Position: refs/heads/master@{#474153}
> Committed: https://chromium.googlesource.com/chromium/src/+/cca67d31f4a0b4ec2c20090a8bfc38c464274ab2

TBR=aboxhall@chromium.org,hayato@chromium.org,dglazkov@chromium.org,esprehn@chromium.org,dmazzoni@chromium.org,kochi@chromium.org
BUG=692360,725815

Review-Url: https://codereview.chromium.org/2902133002
Cr-Commit-Position: refs/heads/master@{#474259}
38 files changed