Stop leaking callbacks in pipeline_impl_unittest.cc
Stop leaking callbacks in pipeline_impl_unittest.cc

BUG=none
TEST=media_unittests under valgrind stops complaining about leaked memory in PipelineStatusNotification's tests.
TBR=acolwell

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@78389 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser