[ced] Suppress a compiler warning on Windows

Add a new option suppressing MSVC compiler warning:

'<': signed/unsigned mismatch  (/wd4018)

where a signed int is used for a loop variable against
unsigned int upper limit. This is a prerequisite to
hooking ced to Blink. The change to gn build file was
already made. This CL applies the same change to gyp.

BUG=597488

Review-Url: https://codereview.chromium.org/2103793005
Cr-Commit-Position: refs/heads/master@{#402728}
1 file changed