Fixed wrong method signatures in TimerReporterMock.

TimerReporterMock had some wrong method signatures, and was lacking signatures
for its accessor methods.

BUG=chromium-os:18800
TEST=None

Change-Id: I08d832857c1ae3df907f5470433117f7a03fe125
Reviewed-on: http://gerrit.chromium.org/gerrit/6230


Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Reviewed-by: Bruno Pontes Soares Rocha <bpontes@chromium.org>
Tested-by: Bruno Pontes Soares Rocha <bpontes@chromium.org>