DevTools: fix valgring warning

This patch fixes valgrind warning "Conditional jump or move depends on
uninitialised value(s)".

BUG=399925
R=vsevik
TBR=vsevik

Review URL: https://codereview.chromium.org/432663003

git-svn-id: svn://svn.chromium.org/blink/trunk@179553 bbb929c8-8fbe-4397-9dbb-9b2b20218538