Refactored HSTSList to use HashMap, where the key of HashMap is the base
domain. Every time when we check if a host is secure, we find the base
domain of the host and get a vector of HSTS entries associated with the
base domain.
While this will not give O(1) look up time, we would have a smaller list
to iterate for every lookup. I have added one unit test to validate
HashMap changes.
Use constructor pattern instead of separate utility function.
Instead of allowing the Servo HSTS file loading to silently fail, we
should expect that file to always exist and be formatted correctly.
In rust-url 1.0 the `Url` struct is going to have private fields, and there
is no way to to create an aribitrary one without going through the parser.
The plugin never had a clear demonstrated performance benefit,
it was made mostly because it was possible and relatively easy at the time.
