This change might make our grammar less perfect, but it will increase our
sanity.

Previously, we were getting double padding: both inside and outside the button.
This patch moves all the padding inside the button so that the whole region is
hittable and the text is positioned correctly.

Fixes #6059

This widget lets you apply an ImageFit to a child widget.

Fixes #5830

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

Fixes #5873

This property now applies only to the free space in the flex layout (i.e.,
minimize or maximize the amount of free space). Previously, the flexible
children were always allocated a size of zero when MainAxisSize was min. Now
they're allocated the same size that would be if the MainAxisSize was max.

Renames stretch constructor to fill for better consistency with
the rest of the framework.

Fixes #5835.

Previously, flexible children were always required to fill their allocated
space. After this change, they can fit loosely into that space and not fill it.
When that happens, the remaining free space is allocated according to the
maixAxisAlignment.

Fixes #5858

See #4434.

Fixes #4618.

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

Fixes https://github.com/flutter/flutter/issues/5283

Other changes in this patch:

Rename OffStage to Offstage.
Fixes https://github.com/flutter/flutter/issues/5378

Add a lot of docs.

Some minor punctuation and whitespace fixes.

Fixes https://github.com/flutter/flutter/issues/5380

Added a flag that instructs Stack how to deal with overflowing
children: they can either be clipped or not.

* Added custom radii to RRect.

This is the first commit towads an implementation of
MergeableMaterial. It adds custom radii to RRect.

* Renamed RRect constructors and added BorderRadius.

BorderRadius is a class similar to EdgeInsets that lets you define
all rounded corners of a rounded rectangle easily.

Also, add a few more debugging flags.

The new `empty_statements` lint (in the next DEV roll), flags these empty statements.  Harmless, except the one in `basic.dart` that fixes a real-life bug. :)

* Change how navigator prevents redundant operations

Instead of requiring transactions, we now cancel all active pointers that are
interacting with the navigator and absorb future pointers until we get a chance
to build. This approach isn't perfect (e.g., events that trigger off the
cancelled pointers could still interact with the navigator), but it should be
better than the current transaction-based approach.

Fixes #4716

* Remove openTransaction

* test

* fixup

Overview
========

This patch refactors images to achieve the following goals:

* it allows references to unresolved assets to be passed
  around (previously, almost every layer of the system had to know about
  whether an image came from an asset bundle or the network or
  elsewhere, and had to manually interact with the image cache).

* it allows decorations to use the same API for declaring images as the
  widget tree.

It requires some minor changes to call sites that use images, as
discussed below.

Widgets
-------

Change this:

```dart
      child: new AssetImage(
        name: 'my_asset.png',
        ...
      )
```

...to this:

```dart
      child: new Image(
        image: new AssetImage('my_asset.png'),
        ...
      )
```

Decorations
-----------

Change this:

```dart
      child: new DecoratedBox(
        decoration: new BoxDecoration(
          backgroundImage: new BackgroundImage(
            image: DefaultAssetBundle.of(context).loadImage('my_asset.png'),
            ...
          ),
          ...
        ),
        child: ...
      )
```

...to this:

```dart
      child: new DecoratedBox(
        decoration: new BoxDecoration(
          backgroundImage: new BackgroundImage(
            image: new AssetImage('my_asset.png'),
            ...
          ),
          ...
        ),
        child: ...
      )
```

DETAILED CHANGE LOG
===================

The following APIs have been replaced in this patch:

* The `AssetImage` and `NetworkImage` widgets have been split in two,
  with identically-named `ImageProvider` subclasses providing the
  image-loading logic, and a single `Image` widget providing all the
  widget tree logic.

* `ImageResource` is now `ImageStream`. Rather than configuring it with
  a `Future<ImageInfo>`, you complete it with an `ImageStreamCompleter`.

* `ImageCache.load` and `ImageCache.loadProvider` are replaced by
  `ImageCache.putIfAbsent`.

The following APIs have changed in this patch:

* `ImageCache` works in terms of arbitrary keys and caches
  `ImageStreamCompleter` objects using those keys. With the new model,
  you should never need to interact with the cache directly.

* `Decoration` can now be `const`. The state has moved to the
  `BoxPainter` class. Instead of a list of listeners, there's now just a
  single callback and a `dispose()` method on the painter. The callback
  is passed in to the `createBoxPainter()` method. When invoked, you
  should repaint the painter.

The following new APIs are introduced:

* `AssetBundle.loadStructuredData`.

* `SynchronousFuture`, a variant of `Future` that calls the `then`
  callback synchronously. This enables the asynchronous and
  synchronous (in-the-cache) code paths to look identical yet for the
  latter to avoid returning to the event loop mid-paint.

* `ExactAssetImage`, a variant of `AssetImage` that doesn't do anything clever.

* `ImageConfiguration`, a class that describes parameters that configure
  the `AssetImage` resolver.

The following APIs are entirely removed by this patch:

* `AssetBundle.loadImage` is gone. Use an `AssetImage` instead.

* `AssetVendor` is gone. `AssetImage` handles everything `AssetVendor`
  used to handle.

* `RawImageResource` and `AsyncImage` are gone.

The following code-level changes are performed:

* `Image`, which replaces `AsyncImage`, `NetworkImage`, `AssetImage`,
  and `RawResourceImage`, lives in `image.dart`.

* `DecoratedBox` and `Container` live in their own file now,
  `container.dart` (they reference `image.dart`).

DIRECTIONS FOR FUTURE RESEARCH
==============================

* The `ImageConfiguration` fields are mostly aspirational. Right now
  only `devicePixelRatio` and `bundle` are implemented. `locale` isn't
  even plumbed through, it will require work on the localisation logic.

* We should go through and make `BoxDecoration`, `AssetImage`, and
  `NetworkImage` objects `const` where possible.

* This patch makes supporting animated GIFs much easier.

* This patch makes it possible to create an abstract concept of an
  "Icon" that could be either an image or a font-based glyph (using
  `IconData` or similar). (see
  https://github.com/flutter/flutter/issues/4494)

RELATED ISSUES
==============

Fixes https://github.com/flutter/flutter/issues/4500
Fixes https://github.com/flutter/flutter/issues/4495
Obsoletes https://github.com/flutter/flutter/issues/4496

Add `@required` for some required parameters in `RRect`. Use elvis
operator to simplify a function.

Fixes 3544

This patch starts working through the missing dartdocs in widgets.dart.

All of the public APIs in rendering.dart now have dartdocs.

This introduces the key parts of a paginated data table, not including
the built-in pagination features.

* Provide more data for the data table demo, so there's data to page.

* Introduce a ChangeNotifier class which abstracts out
  addListener/removeListener/notifyListeners. We might be able to use
  this to simplify existing classes as well, though this patch doesn't
  do that.

* Introduce DataTableSource, a delegate for getting data for data
  tables. This will also be used by ScrollingDataTable in due course.

* Introduce PaginatedDataTable, a widget that wraps DataTable and only
  shows N rows at a time, fed by a DataTableSource.

I pulled the trigger to land the previous patch too quickly and missed a
number of comments.

We used to use this mechanism to paint scrollbars, but it's awkward. The
new approach to scrollbars is much cleaner. This mechanism has no other
clients, so we should remove it.

For consistency.

Fixes #4142

Also, clean up the DatePicker to use more modern technology, such as a
grid for displaying the days of the month.

Fixes #3976

This reverts commit 55f9145e.

Turns out that this commit breaks apps that use the material library,
because of the _errorTextStyle DefaultTextStyle which has inherit:true.
Just setting it to false doesn't work, unfortunately, because then you
hit some sort of issue with merging that text style with others that
have inherit:true.

To make it clear that this constructor requires an explicit style. Also
throw a descriptive error recommending the inherit constructor for
styles with the inherit bit set.

Fixes #3842

The context and child arguments are required.  We should assert that
they're non-null.

Fixes #3843