Enable multiprocess and sandbox

Enable multiprocess and sandbox for Mac and Linux when running
browserhtml.

python/servo/package_commands.py

@@ -146,7 +146,7 @@ def package(self, release=False, dev=False, android=None, debug=False, debugger=
             print("Writing run-servo")
             bhtml_path = path.join('${0%/*}/../Resources', browserhtml_path.split('/')[-1], 'out', 'index.html')
             runservo = os.open(dir_to_app + '/Contents/MacOS/run-servo', os.O_WRONLY | os.O_CREAT, int("0755", 8))
-            os.write(runservo, '#!/bin/bash\nexec ${0%/*}/servo ' + bhtml_path)
+            os.write(runservo, '#!/bin/bash\nexec ${0%/*}/servo -M -S ' + bhtml_path)
             os.close(runservo)
 
             print("Creating dmg")
@@ -220,7 +220,7 @@ def package(self, release=False, dev=False, android=None, debug=False, debugger=
                     delete(dir_to_package + '/build/' + f)
             print("Writing runservo.sh")
             # TODO: deduplicate this arg list from post_build_commands
-            servo_args = ['-w', '-b',
+            servo_args = ['-w', '-b', '-M', '-S'
                           '--pref', 'dom.mozbrowser.enabled',
                           '--pref', 'dom.forcetouch.enabled',
                           '--pref', 'shell.builtin-key-shortcuts.enabled=false',

python/servo/post_build_commands.py

@@ -111,6 +111,10 @@ def run(self, params, release=False, dev=False, android=None, debug=False, debug
                 # Convert to a relative path to avoid mingw -> Windows path conversions
                 browserhtml_path = path.relpath(browserhtml_path, os.getcwd())
 
+            if not is_windows():
+                # multiprocess + sandbox
+                args = args + ['-M', '-S']
+
             args = args + ['-w',
                            '--pref', 'dom.mozbrowser.enabled',
                            '--pref', 'dom.forcetouch.enabled',