Also, fix an issue where hint text wasn't visible when the
InputDecoration was collapsed.

Fixes #8541

This patch prepares us to remove InputValue in favor of TextEditingValue.

Covers lib/ in package:flutter.

Answers http://stackoverflow.com/questions/41371449/how-do-you-use-a-textpainter-to-draw-text

Overflow handling works with clipping, adding an ellipsis on the last
line, or fading the last line.

Fixes https://github.com/flutter/flutter/issues/7271

The indexes passed to paragraph.getBoxesForRange are based on UTF-16 code
units.  If the caret is at a character that is encoded as multiple code units,
then the start and end indexes should be adjusted accordingly.

Fixes https://github.com/flutter/flutter/issues/6154

Fixes https://github.com/flutter/flutter/issues/4478

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

Fixes #5873

This commit renames all debugAssertValid methods to
debugAssertIsValid and assert BoxConstaints validity in
constructors. Fixes #5807.

As of `1.18.0-dev-0`, these cases will get flagged.  In the meantime, the

Assigning to `size` called our intrinsic sizing functions re-entrantly, which
is a destructive operation on TextPainter. Ideally we'd made that a
non-destructive operation, but in the meantime we can fix the tab fading issue
by grabbing the text size before assigning to `size`.

Fixes #4365

It's safe to remove the unneeded `void`s from setters since the blocking issues in the
`always_declare_return_types` lint have been fixed (https://github.com/dart-lang/linter/).  We can also safely flip the bit on  `avoid_return_types_on_setters`.

TextAlign applies to a whole paragraph instead of applying to an individual
text span. This patch moves the property out of TextStyle and into a separate
property on Text and RichText.

Instead of using properties, TextPainter now receives min and max width as
parameters to layout. Also, this patch integrates the intrinsic sizing logic
into the main layout function, which satisfies all the existing uses cases.

Fixes #3503

We're getting back to the point where we have a bunch of foundation APIs
and it's getting confusing having them mixed with services/.

Fixes #1541

We'll eventually remove Paragraph#paint.

Fixes #2694

And fix the zillion issues that uncovered.

This reverts commit f41b3411, reversing
changes made to e33d8d96.

This was a bad check-in due to my mangling uploading a new version of the branch from a different machine.

This reverts https://github.com/flutter/flutter/pull/2639 and will be replaced by https://github.com/flutter/flutter/pull/2640

And fix the zillion issues that uncovered.

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

Currently the interface for recognizing gestures on text spans is pretty ugly,
but hopefully we can improve it with time.

Fixes #156

We forgot to compare the lengths of the lists.

Now we just have one TextSpan class that handles both simple strings, trees of
children, and styling both. This approach simplifies the interface for most
clients.

This patch also removes StyledText, which was weakly typed and tricky to use
correctly. The replacement is RichText, which is strongly typed and uses
TextSpan.

Each layer is supposed to reexport the parts of the previous layer
that are part of its API.

- In painting.dart, export from dart:ui all the Canvas-related APIs
  that make sense to be used at higher levels, e.g. PaintingStyle.

- Delete painting/shadows.dart. It was dead code.

- In rendering/object.dart, export all of painting.dart.

- In widgets/basic.dart, export all of painting.dart and
  animation.dart. Some classes in animation/ are renamed to make this
  less disruptive and confusing to the namespace.

- Split out Stocks back into an import model rather than a part model,
  so that it's easier to manage its dependencies on a per-file basis.

- Move Ticker to scheduler library.

- Remove as many redundant imports as possible now.

- Some minor nit picking cleanup in various files.

Now the text input control knows how to move the caret when you tap
inside the string. There's still some rough edges to polish up, but this
patch is the first step.

Fixes #108

This patch teaches the editing system to paint reasonable selections for
single-line text fields, including for bidirectional text.

Requires https://github.com/flutter/engine/pull/2318

Also, some trivial fixes for things that I found while playing with
the rendering library directly.