Implement IPC::ParamTraits for PlatformSharedMemoryRegion

This CL adds the support for passing PlatfromSharedMemoryRegions
between processes via IPC messages.

Bug: 795291
Change-Id: I13b22226866b0a4e5d97e66f4ce93e5ad28fdaac
Reviewed-on: https://chromium-review.googlesource.com/937514
Commit-Queue: Alexandr Ilin <alexilin@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Matthew Cary <mattcary@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552192}
13 files changed