Mojo JS standalone app launches files specified with mojo_shell command-line args
Arguments specified with the mojo_js_standalone app URL are loaded and run. Each argument is run on a separate thread, in its own V8 isolate. For example:
mojo_shell 'mojo:mojo_js_standalone foo.js bar.js'
Also: moved the one-time gin V8 initialization from JSApp - where it could be called from multiple threads - to ApplicationDelegateImpl::Initialize(). Where it's called once, before any JSApp's are started.
BUG=419906
Review URL: https://codereview.chromium.org/
627563002
Cr-Commit-Position: refs/heads/master@{#298032}