Fix styleguide violations from https://codereview.chromium.org/1681363003

* Don't use default capture (luckily not needed here)
* Don't use std::function -- since nothing's captured, the lambda can decay
  to a function pointer here

No behavior change.

BUG=none

Review URL: https://codereview.chromium.org/1705123004

Cr-Original-Commit-Position: refs/heads/master@{#375990}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 08feeb7e4150acb4dd1af413555023660682c3c8