* justifyContent -> mainAxisAlignment
* alignItems -> crossAxisAlignment
* FlexJustifyContent -> MainAxisAlignment
* FlexAlignItems -> CrossAxisAlignment

Fixes #231

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.

One bug was masking the other, hence they both needed to be fixed
and tested separately.

@Hixie

...so that it's easier to copy/paste between the rendering and settings layers.

The asserting will continue until morale improves!

* Convert all assert(*.isNormalized) checks to use the new
  debugAssertIsNormalized technology.
* Convert CustomMultiChildLayout to use the new RenderingError
  technology to greatly improve the detail in errors you get when
  writing CustomMultiChildLayout delegates.
* Add BoxConstraints.copyWith().
* Indent the descendants in the rendering exception data dump so that
  when you have multiple children it's clearer what's going on.

There aren't any clients anymore.

Fixes #1684

Previously we used Position, which makes it harder to accumulate offsets
when walking the render tree.

Add BoxConstraints.isNormalized feature.

Use this feature in asserts in all the intrinsic dimension methods, in
various relevant BoxConstraints methods, and in layout().

Wrap the _DebugSize logic in BoxConstraints.constrain() in an assert
block to avoid a branch in release mode.

Remove the logic in BoxConstraints.isSatisfiedBy() that dealt with
non-normalized values.

Add BoxConstraints.normalize().

Make RenderCustomOneChildLayoutBox.performLayout() only set
parentUsesSize on the child if the constraints aren't tight.

Previously, we would assert with FlexJustifyContent.collapse if we ran out of
space. Now we do the same thing we do for the other types of justification,
which is to let the children's layout overflow.

This pattern breaks when using compositing because we need to lift those
operations into the compositing tree. This patch removes all the ones I could
find and adds an assert to help prevent more from getting introduced.

Fixes #191

Now a RenderBox is considered hit if one of its children are hit or it itself
decides that it's hit. In particular, empty space inside a flex won't be hit
because none of the children are located there and a RenderFlex doesn't
consider itself hittable.

Fixes #53
Fixes #1221

- change how we expose settings at the RenderObject layer so that it's
  easier to maintain.
- expose the Widget owner chain in the RenderObject layer debug output
- add debug info to RenderOpacity, RenderIgnorePointer, RenderListener
- make the output for text nodes prettier

Add type annotations in many places.
Fix some identifiers to have more lint-satisfying names.
Make all operator==s consistent in style.
Reorder some functions for consistency.
Make ParentData no longer dynamic, and fix all the code around that.

Now that you import a top-level file for each layer of the Flutter
framework, within the framework we can use relative paths without being
worried about the copy/pasta problem we used to have.

All the use cases for EventDisposition are now addressed by the gesture
detection system.

We need a short name more often than a tree dump, so toString() should
be the short name.

Make debugDumpRenderTree() a global like debugDumpApp(), for
consistency. It's hard to remember the
SkyBinding.instance.dumpRenderTree() incantation.

Fixes #1179.

This reverts commit 7592213df29066cd357eaa4fffe4a19ed3bae189.

Along with some other docs.

These needed to be updated because we moved the widgets directory into the src
directory to hide it from dartdoc.

Rather than reading out the maxWidth, we should call constrainWidth to factor
in the minWidth, which might be bigger.

Code outside of package:sky should import this code using

package:sky/rendering.dart
package:sky/widgets.dart

Moving this code into the "src" directory is a convention that signifies that
and it cleans up the generated dartdoc because the libraries in the src
directory aren't included in the generated documentation. Instead, the classes
are documented in the widgets.dart and rendering.dart libraries.

This patch makes ParentDataNode less general purpose and instead teaches Flex
and Stack how to program the parent data for their children. We used to have
this general system because parent data used to carry CSS styling, but we don't
need it anymore.

Fixes #957

We were setting the main axis extent to zero because we had a sign error.

Fixes #918

This hopefully explains things well enough that it fixes #846, after a manner.

This still leaves Flex and FlexDirection available. At some point once
people have transitioned to Row/Column we should rename Flex to _Flex
and stop reexporting FlexDirection from basic.dart.

- Catch exceptions closer to the source.
- Factor out exception printing code.
- Have widget library hand the rendering library some context when syncing RenderObjectWrappers to aid with debugging.
- Fix a bug in flex.dart whereby _overflow was compared when null.

Fixes #698 to actually work.
Also, adds some debugging aids around Flex.
And a test to check this fix.

We'll need this for compositing because we need to switch out the sky.Canvas
when we switch compositing layers.