Clean up AppRegistrar and AppRegistrarObserver

This is a follow up CL to https://chromium-review.googlesource.com/c/chromium/src/+/1592977
to address some minor coding nits.

Bug: 891172
Change-Id: Ie2368ce9a06224f0c03609d6c54d1a2d2e0f1286
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1597518
Commit-Queue: Alan Cutter <alancutter@chromium.org>
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657528}
2 files changed