GitLab

Turn on sandbox for mojo apps by default. Apps that need to run
without a sandbox need to include 'shell:unsandboxed' in their
capabilities in manifest for mojo:shell.

Update manifests for mojo:ui, mojo:font_service, mojo:file_system,
and mojo:leveldb services to include 'shell:unsandboxed'.

BUG=645602, 646376

Review-Url: https://codereview.chromium.org/2338793003
Cr-Commit-Position: refs/heads/master@{#419891}