Reland Enable crashpad for Mac.
-- Add :mac_helpers dependendency to headless_lib

Original reason for revert: Reason for revert:
mac_chromium10.10_rel_ng buildbot failing in browsertests
https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.mac%2FMac10.10_Tests%2F16541%2F%2B%2Frecipes%2Fsteps%2Fheadless_browsertests_on_Mac-10.10%2F0%2Flogs%2FCrashReporterTest.GenerateMinidump%2F0

This follows the same logic as using breakpad in linux with flags --enable_crash-reporter and --crash-dumps-dir folders.

For headless_shell target, we need to include the Helper crashpad_handler in the build. For --headless, this is already available in the framework bundle.

BUG=687407

Review-Url: https://codereview.chromium.org/2816593006
Cr-Commit-Position: refs/heads/master@{#464289}
Committed: https://chromium.googlesource.com/chromium/src/+/ecb2ad24952b077e71e56ba9d3edfc83c522f32a

patch from issue 2816593006 at patchset 60001 (http://crrev.com/2816593006#ps60001)

Review-Url: https://codereview.chromium.org/2820453003
Cr-Original-Commit-Position: refs/heads/master@{#465869}
Committed: https://chromium.googlesource.com/chromium/src/+/df51c3e48120bc5f68e0fc2cdc92d91592249e98
Review-Url: https://codereview.chromium.org/2820453003
Cr-Commit-Position: refs/heads/master@{#466275}
3 files changed