Keep only base/extractor.[cc|h].

Change-Id: I2fd15eeae9fcba3f33d10317bba92634959860d8
Reviewed-on: https://chromium-review.googlesource.com/220982
Reviewed-by: Jack Hou <jackhou@chromium.org>
Commit-Queue: Jack Hou <jackhou@chromium.org>
Tested-by: Jack Hou <jackhou@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Commit-Queue: Ben Wells <benwells@chromium.org>