Mac: Add support for in-process crash reporting to Breakpad.

Add new option BREAKPAD_IN_PROCESS.
If YES, Breakpad will write the dump file in-process and then launch the reporter
executable as a child  process.

Originally reviewed at https://codereview.chromium.org/571523004/

BUG=chromium:414239
R=mark@chromium.org

Review URL: https://breakpad.appspot.com/1714002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1375 4c0a9323-5329-0410-9bdc-e9ce6186880e