ipc: Update Windows attachment brokering ownership semantics.

I updated the semantics to match the Mac attachment brokering semantics,
which are much more precise. This fixes a HANDLE leak.

BUG=493414

Review URL: https://codereview.chromium.org/1494313002

Cr-Commit-Position: refs/heads/master@{#363296}

• ipc/attachment_broker_privileged.h[diff]
• ipc/attachment_broker_privileged_win.cc[diff]
• ipc/attachment_broker_privileged_win_unittest.cc[diff]
• ipc/attachment_broker_unprivileged_win.cc[diff]
• ipc/handle_attachment_win.cc[diff]
• ipc/handle_attachment_win.h[diff]
• ipc/handle_win.h[diff]
• tools/metrics/histograms/histograms.xml[diff]