DevTools: Use InspectorFrontendHostStub if IFH is missing an invoked method

R=kaznacheev, pfeldman
NOTRY=true
BUG=363608

Review URL: https://codereview.chromium.org/239253002

git-svn-id: svn://svn.chromium.org/blink/trunk@171671 bbb929c8-8fbe-4397-9dbb-9b2b20218538