Clean-up the SandboxSyscall interface

Create a new Syscall class with a static method to replace SandboxSyscall()
and clean-up some documentation.

BUG=369594

Review URL: https://codereview.chromium.org/330723003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@277004 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed