[clear-site-data-tests] Add basic tests for the Clear-Site-Data header (#4317)

Clear-Site-Data (https://www.w3.org/TR/clear-site-data/) is a header
instructing the user agent to delete certain datatypes.

This commit adds the testing infrastructure (a server serving this
header and JS utility functions), and a basic test verifying that
the header is respected for cookies and storage deletions on
a navigation.

Cache tests will be added in a followup change. Subresource request
tests are not yet added, as they are not implemented by any browser.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/4317

Received on Monday, 12 December 2016 15:36:50 UTC