DevTools: fix gypi to recompile InjectedScriptSource

This patch fixes gypi to recompile InjectedScriptSource.h
as soon as InjectedScriptSource.js changes

BUG=
TBR=pfeldman

Review URL: https://codereview.chromium.org/27019007

git-svn-id: svn://svn.chromium.org/blink/trunk@159591 bbb929c8-8fbe-4397-9dbb-9b2b20218538