The sql connection memory dump is not thread safe since the connections
can get deleted while a dump is happening. To make this thread safe,
this CL introduces a dump provider class owned by the connection. This
class holds a lock when dumping and deleting the database. Also, to
workaround thread safe dump provider registration, it uses the
UnregisterAndDeleteDumpProviderAsync api added in crrev.com/1430073002.

BUG=466141

Review URL: https://codereview.chromium.org/1434993002

Cr-Commit-Position: refs/heads/master@{#369161}