Auto merge of #12708 - paulrouget:multiprocessAndSandboxForBhtml, r=metajack

Enable multiprocess and sandbox

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---
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- [ ] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #12705 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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

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python/servo/package_commands.py

@@ -146,7 +146,7 @@ class PackageCommands(CommandBase):
             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 @@ class PackageCommands(CommandBase):
                     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 @@ class PostBuildCommands(CommandBase):
                 # 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',