[tracing] Fix MemoryDumpManager testing instance teardown pattern.

[tracing] Fix MemoryDumpManager testing instance teardown pattern.

crrev.com/933613002 introduced a ODR violtaion by adding the
DeleteForTesting method (other definition in trace_event_impl.cc).
This was causing an ASan assertion (see crbug.com/459556) and failures
of base_unittests in debug builds (see crrev.com/933613002 #33).
This CL fixes the DeleteForTesting pattern removing the awkward ODR
violation.

BUG=459556, 458295
TBR=nduca@chromium.org

Committed: https://crrev.com/97206c26057c11573bf6aea8aff40ee345874648
Cr-Commit-Position: refs/heads/master@{#317316}

[Primiano Tucci (use gerrit), 2015-02-20 10:36:44]

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

[Sami, 2015-02-20 12:16:42]

Thanks, lgtm.

[Sami, 2015-02-20 12:16:50]

The CQ bit was checked by skyostil@chromium.org

[commit-bot: I haz the power, 2015-02-20 12:17:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/942803002/20001

[commit-bot: I haz the power, 2015-02-20 14:31:23]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-20 14:32:06]

Patchset 2 (id:??) landed as
https://crrev.com/97206c26057c11573bf6aea8aff40ee345874648
Cr-Commit-Position: refs/heads/master@{#317316}