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This CL makes the check for unregistering dump providers on right thread
stricter by checking even if tracing is not enabled. This is made
stricter only for new dump providers while the existing ones (except few
which are verified correct) are added to a blacklist which does not hit
this check. In next CLs this blacklist will be cleared not to cause
flakiness on the bots with lots of dump providers failing.

BUG=643438

Review-Url: https://codereview.chromium.org/2592233002
Cr-Commit-Position: refs/heads/master@{#442777}