The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2fc6cf8d316d1f452dd27dbd0d886aef15b69659

commit 2fc6cf8d316d1f452dd27dbd0d886aef15b69659
Author: lawrencewu <lawrencewu@chromium.org>
Date: Sat Dec 10 01:27:20 2016

Add POSIX shared memory support for Mac

This re-adds POSIX shared memory support on Mac. This
is for use in the sharing of field trials using shared memory. You
can see the design doc for this project at:
https://docs.google.com/document/d/1mTjD99PchmCGYtLvpxaXFObVnid1zmXIsWBI7GjuJgo/
and the motivation for this change under "Port to other platforms".

NOTE: turning on NOPRESUBMIT because this re-adds some banned calls to AllowIO.

BUG= 671228 
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2555483002
Cr-Commit-Position: refs/heads/master@{#437709}

[modify] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/BUILD.gn
[modify] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/memory/shared_memory.h
[modify] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/memory/shared_memory_handle.h
[modify] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/memory/shared_memory_handle_mac.cc
[add] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/memory/shared_memory_helper.cc
[add] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/memory/shared_memory_helper.h
[modify] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/memory/shared_memory_mac.cc
[modify] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/memory/shared_memory_posix.cc
[modify] https://crrev.com/2fc6cf8d316d1f452dd27dbd0d886aef15b69659/base/memory/shared_memory_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/73172f9e94e5af7e23867506c9e5a9d6bc99c703

commit 73172f9e94e5af7e23867506c9e5a9d6bc99c703
Author: hajimehoshi <hajimehoshi@chromium.org>
Date: Wed Dec 14 04:57:48 2016

Add a macro for SharedMemory::Share

SharedMemory::Share was introduced at crrev.com/2555483002 only on Mac
and not other platforms. This CL adds a macro to SharedMemory::Share
declaration to clarily that the function Share is available only on Mac.

BUG= 671228 
TEST=n/a

Review-Url: https://codereview.chromium.org/2567293003
Cr-Commit-Position: refs/heads/master@{#438434}

[modify] https://crrev.com/73172f9e94e5af7e23867506c9e5a9d6bc99c703/base/memory/shared_memory.h