Use unique_ptr<> for BrowserPluginGuest creation APIs

Bug: 419087
Change-Id: Ic870c7059fef752560d0299064a0cef4a1733f3a
Reviewed-on: https://chromium-review.googlesource.com/c/1277594
Commit-Queue: Albert J. Wong <ajwong@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599077}
4 files changed