DevTools: Fix Windows debug_devtools=1 builds

This patch eliminates the "Command line too long" errors
when building on Windows in the debug_devtools=1 mode.

Drive-by: Fix GN build after r183969

R=pfeldman, vsevik

Review URL: https://codereview.chromium.org/665083002

git-svn-id: svn://svn.chromium.org/blink/trunk@184003 bbb929c8-8fbe-4397-9dbb-9b2b20218538