Pull a newer mojo_services

This patch picks up a new url_loader.mojom interface that is needed to access
the network in production.

Cleanups to network service

This patch contains some minor improvements to the network service:

- We now cache the connection to the network service so we don't need to spin
  it up for each request.
- We now manage the lifetime of NetworkServiceImpl in the same way as other
  services.

Also, update the workbench sky_tools dependency to the latest version.

Add bindings for "GL_NV_texture_barrier" required on Mac

Teach big_red_button how to publish sky, sky_engine, sky_services

This CL makess big_red_button.py work for the sky, sky_engine, sky_services
packages.

Complete OpenGL setup and input event handling on Mac

Enable scrollable tabs fling scrolling

We need to pull in an updated version of sky_tools to get a version that
doesn't try to gzip everything.

Fix sky_tool's installing of SkyShell.apk

We were walking over to the realdir too quickly, which meant we lost which
version of the sky_engine package we were supposed to use.

Teach ./sky/tools/gn where to run the gn binary

Remove Location.idl and assoicated code

Remove Screen.idl and associated code

Remove the DOM-based custom layout machinery

Run the Dart analyzer on Travis

We now do layout without a DOM.

Scoped focus, so you can have a dialog with input controls and not lose your focus in the background

Scoped focus, so you can have a dialog with input controls and not lose your focus in the background.

This introduces a GlobalKey registry so that you can tell when a key
has gone away (so you can unfocus dead dialogs).

Also I added an assert that you're not calling setState() during a
build. It turns out that doing so means you have a bug, because since
you're dirty already (you're building), you won't get rebuilt.

The focus code itself is gnarly. It uses a Component and an internal
Inherited TagNode to manage the focus state, and does crazy things
like updating its state during build to pretend retroactively that it
was built with some other state, once someone asks for focus the first
time (i.e. the first time it's examined, so you can't tell that it was
in a different state before). It does this so that it can autofocus
controls which otherwise wouldn't be focused.

This moves all the focus management into Navigator and showDialog(),
so the complexity is all buried deep and not visible to apps,
hopefully.

To do something like two tabs that each have an Input widget that
needs to be focused when you switch panes, you'd need to have two
Focus objects, one in each tab, and you need to set their autofocus to
true (maybe that should be the default?).

Fix review feedback from previous checkin.

@abarth doesn't like Futures that explicitly point out they're type-unsafe. :-P

Fix the lerp the RIGHT way.

Fix the crash for buttons.

pushDialog(navigator, (navigator) => new Dialog(...)).then((result) => process(result));

Turns out there was a typo in lerpColor.

Fixes #277.

Move fitness dialog into its own class