Snackbar opacity animation shouldn't trigger on reverse

Tab updates

Fixes #617

Update engine

Make it possible to dismiss a snackbar manually

Fixes #463

This patch updates our use of Mozart to the latest version of the protocol.

add services to schema

Fixes the broken Weather demo

DatePicker et al updates

These height values are incorrect

They're actually leading values rather than line height values, which means
they're operative between paragraphs not within a given paragraph.

fix image loading

Improve docs for TextStyle#height

Fixes #2918

Update engine

rev mockito; remove deprecated uses

Also, pass font information to ui.ParagraphStyle.

run pub with --no-package-symlinks

The intrinsic size checks were very slow

Now we run them once per render object.

Fixes #2487

Reactivating a StatefulElement should imply a build

Fixes #2901

More table fixes

Animate TwoLevelList leading icon color

Add keys to ResourceImages.

[driver] fix observatory port # and timeline data extraction

The way we pick observatory port # has changed and we have broken
logic that handles port 8181. To fix the buildbot, switch to port
8182. We can later figure out what we want to do when we clean up
port handling.

The old VM extention for extracting the timeline data is gone.
Switch to the new '_getVMTimeline' API.

Use _ScaffoldLayout to position scroll-resizable appbars