Roll NDK to r11c and extract it into its own repository.

BUG=599327

Change-Id: Ifd0f6e16991e6825859761027917b2171b260258
Reviewed-on: https://chromium-review.googlesource.com/346782
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Tested-by: John Budorick <jbudorick@chromium.org>