Include string.h for strncmp in ExtensionBehavior.cpp
Include string.h for strncmp in ExtensionBehavior.cpp

BUG=angleproject:2147

Change-Id: I53062a84d48e1c106901a8c32fa49b0148baa344
Reviewed-on: https://chromium-review.googlesource.com/664059
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Commit-Queue: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

ppy/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle,MSOpenTech/angle,ppy/angle