Embedder handling of prompts and alerts
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Allow embedder to allow alerts and prompts, but via constellation forwarding messages from script.
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Automatically provide a resource reader for tests
Fix#20710
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Made the memory cache data structure derive MallocSizeOf, along with
manual size_of() implementations in malloc_size_of.
Added a Measurable struct that acts as a container for fields size_of() can be called for.
Added a new IpcReceiver used for listening to messages from the memory profiler,
and used run_with_memory reporting to register a memory reporter in the thread.
Now when a message from the memory profiler arrives, report includes sizes of public and private http caches.
Updated test file.
Use specific assertions
Similar to #19865
r? jdm
Note: Should I squash all the commits into one commit?
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Ignore aborted responses in caching
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@jdm @KiChjang @Manishearth Follow up on https://github.com/servo/servo/pull/18676 and https://github.com/servo/servo/pull/19274 to ignore aborted responses in caching.
I also found out the cache shouldn't return any response whose body is still in `ResponseBody::Receiving` mode, because that fails the assertion at https://github.com/servo/servo/blob/master/components/net/fetch/methods.rs#L438(we might want to add a channel as pat of the cached response later on to deal with this case). I only found out now because I needed the response from the server to trickle in so that it could be cached and aborted.
I copied the `http-cache.py` server from the wpt folder, and added a 'trickle' option, which is necessary to actually have a failing test with a cached but aborted request, it's now passing.
I also remove one unused import that slippled through previously.
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