* globalToLocal was just broken when there was a rotation and a
  translation at the same time. This fixes that and adds a test.

* update graphic used by spinning_mixed since the old one went 404.

* simplify some of the code in the demo.

* fix MatrixUtils.transformPoint to be consistent with how we transform
  points elsewhere.

* stop transforming points elsewhere, just use
  MatrixUtils.transformPoint.

* make the Widget binding handle not having a root element.

* make the spinning_mixed demo update its widget tree.

This version of the engine crashes on startup.

This reverts commit a426b6b3.

This feature is the implementation of an accessibility feature that changes the
size of text by a constant factor.

Fixes #5873

The engine now reports coordinates in physical pixels.

Also, fix an old TODO, and add a test of various things on TextStyle.

...requires an engine roll to pick up https://github.com/flutter/engine/pull/3025 and https://github.com/flutter/engine/pull/3027.

These tests should hit some previously untested lines.

Image listeners installed in paint handlers need to know whether the listener
is being called during the paint.

Fixes https://github.com/flutter/flutter/issues/4937

Also, add FractionalOffset.inscribe.

Previously we lerped them backwards.



Fixes #2832

Fixes #1382

Specifically:

* Handle null styles in TextSpan without crashing in toString().

* Handle null children in TextSpan child lists without crashing in
  toString().

* Handle entirely empty TextSpans in toString() explicitly.

* Assert that TextSpans don't contain nulls in various places. This is
  done more often than one might think necessary, because it turns out
  that TextSpan takes a (mutable) List for one of its arguments, so
  who knows what it will contain at any given time. By asserting all
  over the place, hopefully we'll catch it near the change if they do
  change it.

* Add a RichText example to Stocks to exercise RichText and TextSpans.

See also: https://github.com/flutter/flutter/issues/2514, https://github.com/flutter/flutter/issues/2519

We need to apply the alignment to the source rect because the ouput rect fills
the destination rect.

Fixes #1514

We forgot to compare the lengths of the lists.