Build shared_memory_mac.cc and shared_memory_handle_mac.cc for iOS

Build shared_memory_mac.cc and shared_memory_handle_mac.cc for iOS

media::VideoFrame has new constructors that use SharedMemory and
SharedMemoryHandle. This patch enables building the Mac implementations
to support building //media/cast/sender on iOS.

BUG=528408
Committed: https://crrev.com/cc7516ec9d89cff1d5cfe72794395c1a1c95908e
Cr-Commit-Position: refs/heads/master@{#347569}

[jfroy, 2015-09-04 19:41:04]

jfroy@chromium.org changed reviewers:
+ dalecurtis@chromium.org, miu@chromium.org

[jfroy, 2015-09-04 19:41:59]

jfroy@chromium.org changed reviewers:
+ thakis@chromium.org

[jfroy, 2015-09-04 19:44:28]

jfroy@chromium.org changed reviewers:
+ mark@chromium.org

[miu, 2015-09-04 20:15:07]

lgtm

[Mark Mentovai, 2015-09-04 20:28:25]

LGTM

[DaleCurtis, 2015-09-04 22:26:50]

not an owner for this, but lgtm :)

[jfroy, 2015-09-04 22:48:36]

The CQ bit was checked by jfroy@chromium.org

[commit-bot: I haz the power, 2015-09-04 22:48:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1328963002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1328963002/1

[commit-bot: I haz the power, 2015-09-05 00:11:24]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-05 00:11:25]

Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[jfroy, 2015-09-05 06:57:32]

The CQ bit was checked by jfroy@chromium.org

[commit-bot: I haz the power, 2015-09-05 06:57:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1328963002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1328963002/1

[commit-bot: I haz the power, 2015-09-05 08:47:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-05 08:48:33]

Patchset 1 (id:??) landed as
https://crrev.com/cc7516ec9d89cff1d5cfe72794395c1a1c95908e
Cr-Commit-Position: refs/heads/master@{#347569}