Add MODULES_EXPORT to SyncEvent
Add MODULES_EXPORT to SyncEvent

To fix link error when building core and modules separately.

BUG=358074, 492283

Review URL: https://codereview.chromium.org/1175373002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@196976 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk