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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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because it should not break anything
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