bindings: Reduce size of few headers in platform/bindings/

Clean unused includes and add forward declarations for classes
when possible to reduce size of headers.

* Move implementation of the |Policy::UpdateContainerPolicy| function to
  the policy.cc file to avoid including SecurityOrigin header to policy.h.

Bug: 242216
Change-Id: Ib8923f7715b5f321d52c58ca96a7a4bbaa0dcdc5
Reviewed-on: https://chromium-review.googlesource.com/1125935
Commit-Queue: Andrey Kraynov <iceman@yandex-team.ru>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573881}
28 files changed