base: Use std::move() instead of Pass() for real movable types.

Some of our movable types have real move-constructors/assignment
operators now. We can use std::move() for these types instead of Pass().

There's still some move-only types that are implemented using an
"Rvalue" type emulation, so we have to keep Pass() for those still.

R=thestig@chromium.org
BUG=557422

Review URL: https://codereview.chromium.org/1479473002

Cr-Commit-Position: refs/heads/master@{#361583}
56 files changed