Unreviewed fix for inspector tests in debug.
m_frontend should be initialized in constructor.

* inspector/InspectorMemoryAgent.cpp:
(WebCore::InspectorMemoryAgent::InspectorMemoryAgent):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142086 268f45cc-cd09-0410-ab3c-d52691b4dbfc