Remove some incorrect/obsolete reference to AsyncExtensionFunction.

ChromeAsyncExtensionFunction does not derive from
AsyncExtensionFunction, update such references, mostly in comments.

Bug: 829174
Change-Id: Ic48ec85540f00660ecbb58899d501152c1117341
Reviewed-on: https://chromium-review.googlesource.com/1001772
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549351}
14 files changed