[tracing] Make memory-infra unregristration DCHECK stricter

[tracing] Make memory-infra unregristration DCHECK stricter

This is a follow-up to the discussion started in crrev.com/1430073002 .
There is no reason for DCHECK-ing against unsafe unregistrations
of memory dump providers only when tracing is enabled. A safe
unregistration should always be performed, regardless of the state
of tracing.

BUG=

[Primiano Tucci (use gerrit), 2016-01-04 16:17:25]

primiano@chromium.org changed reviewers:
+ ruuda@google.com

[Primiano Tucci (use gerrit), 2016-01-04 16:18:43]

primiano@chromium.org changed reviewers:
+ oysteine@chromium.org

[Primiano Tucci (use gerrit), 2016-01-04 16:18:43]

+oysteine for OWNERS
I haz no power in //components/tracing and //content/browser/tracing/

[Ruud van Asseldonk, 2016-01-04 18:43:32]

Patchset 2 looks good to me, but it looks like you were right about dumpers
doing unsafe unregistration after tracing is disabled.

[Primiano Tucci (use gerrit), 2016-01-04 18:45:05]

Patchset #3 (id:40001) has been deleted

[oystein (OOO til 10th of July), 2016-01-04 21:45:56]

On 2016/01/04 18:43:32, Ruud van Asseldonk wrote:
> Patchset 2 looks good to me, but it looks like you were right about dumpers
> doing unsafe unregistration after tracing is disabled.

lgtm for //components/tracing and //content/browser/tracing