chrome/browser/extensions: Change auto to not deduce raw pointers.

This patch updates the code to prevent auto deducing to a raw pointer.

[email protected]
BUG=554600

Review-Url: https://codereview.chromium.org/2172043002
Cr-Commit-Position: refs/heads/master@{#407603}
14 files changed