GuestView: Cleanup
This CL uses the new C++11 auto keyword to improve readability of GuestView code. There are two main ways auto is being used in this CL:
1. Iterators. It is verbose to specify the type of an iterator that's fairly self-evident, so we avoid that now.
2. *::From* calls. Some objects are accessible via IDs or some other key. It is self-evident the return type in this case and so it is reasonable to use auto here as well.
BUG=none
Review URL: https://codereview.chromium.org/
857043002
Cr-Commit-Position: refs/heads/master@{#312242}