Currently ProfilerListener holds all the CodeEntries it ever
created during the profiling session. It is not capable of removing
entries corresponding to the code objects discarded by GC as there's
no such code event.

However it is sometimes possible to tell if a code object was GCed.
Hook up to the CodeMap code entry removal and if the entry has never
been hit by a sample we can safely delete it.

As a bonus the CodeEntryInfo size has been reduced on x64, which also
saves 8 x <number of code entries> bytes.

BUG=v8:7719

Change-Id: I988bc5b59f3fba07157a9f472cbcf68596fcd969
Reviewed-on: https://chromium-review.googlesource.com/1054346Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53222}