[handles] Sanitize Handle and friends.
Bunch of cleanups to allow us to get rid of handles-inl.h at some
point (in the not so far future); but more importantly to sanitize uses
of handles and prepare for handle canonicalization support.
R=yangguo@chromium.org
Committed: https://crrev.com/
3283195d0408333cce552cf4087577e6f41054e5
Cr-Commit-Position: refs/heads/master@{#28222}
Committed: https://crrev.com/
d940c6d3bcc227b459cb4123d9a8332d9ed0d5f8
Cr-Commit-Position: refs/heads/master@{#29666}
Review URL: https://codereview.chromium.org/
1128533002
Cr-Commit-Position: refs/heads/master@{#29675}