ChildProcessSecurityPolicy: Change over to custom bitmask set.

Applies on top of https://codereview.chromium.org/25601002/.

Refactoring plan:
https://docs.google.com/a/google.com/document/d/1QGkGWuwgSuaRqovz4wyb0upqPKDVsgYOFKt44E7gmOE/edit?usp=sharing

chromium-dev thread:
https://groups.google.com/a/chromium.org/d/msg/chromium-dev/2cGLolxsOs4/Ga8eF7iEejkJ

R=tsepez@chromium.org
BUG=262142

Review URL: https://codereview.chromium.org/25915002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228744 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228744
Add handling of fatal errors to RawChannel/RawChannelPosix.

Also fix a race if |Shutdown()| were called simultaneously (on the I/O thread)
with |WriteMessage()| being called (and posting |WaitToWrite()|).

R=davemoore@chromium.org

Review URL: https://codereview.chromium.org/27241003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228745 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228745