This moves input.dart to editing2/, since that way we can define the layering as strictly unidirectional.
It also reorders a bunch of imports to fit the style guide.
I removed the old remnants of the widgets example, and put the fn2 examples into the examples/widgets/ directory, to parallel the framework directory names.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1177243002.

Previously, they always started at the center of the RenderInkWell. Now we
remember the local coordinates we computed during the hit test and provide that
information when handling the event.

R=ianh@google.com

Review URL: https://codereview.chromium.org/1180553002.

 - constructors first
 - have either a blank line at the top and bottom of each class, or no blank line in either place (it's still inconsistent about which we should do)
 - hide clamp()

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1172173002

Instead of triggering layout synchronously during AppView construction, we now
schedule the initial layout using a magic bootstrapping function.

TBR=ianh@google.com

Review URL: https://codereview.chromium.org/1172123003.

Add asserts to prevent people from setting box.parentData.position or box.size except during layout.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1176623002

Export Point, Size, Rect, Color, Paint, Path, BoxDecoration, Border, BorderSide, EdgeDims, and FlexDirection from fn2.dart
That way most of our libraries don't have to use sky.Foo all over the place, and we can reduce the number of imports in most Dart components.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1161323004

 - several places where we use a getter knowing that it will return a
   subclass of its declared type, even asserting that it does, but
   where the analyzer is worried that the getter might start returning
   a new value unexpectedly, solved by having a temporary local
   variable shadow the getter and asserting that it doesn't change
   value
 - many many places where we do this with parentData specifically,
   solved by type-erasing parentData.
 - a place where a mixin wants to be subclassing another class, and
   uses its methods, solved by saying that the mixin is abstract but
   implements the superclass

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1160923008

Include DETACHED, NEEDS-LAYOUT, and relayoutSubtreeRoot info in the debug output for the render tree

R=chinmaygarde@google.com

Review URL: https://codereview.chromium.org/1149083011

Improve the RenderObject.toString() logic so that there's not blank lines everywhere and to generally be better.
Adds sizes, positions, transforms, improves RenderParagraph's output.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1160233004

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1151533006

This makes debugging the render tree a lot easier. Just print the node
you care about, and you get an indented tree view of its subtree,
including settings. New subclasses should implement the new virtual
method debugDescribeSettings() to expose new settings.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1157993005

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1144933007

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1165013003

The root cause of the crash was threefold:
 - you can't enumerate enums, in dart; you have to enumerate their values.
 - RenderNodeWrapper was trying to call remove(child.root) on its root, but that's
   not something that all RenderNodes have
 - when a RenderNode was deparented, its relayoutSubtreeRoot wasn't removed, so
   the node ended up in an inconsistent state regarding its parent tree

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1151573020

This CL makes gesture events work again in fn2.

R=ianh@google.com

Review URL: https://codereview.chromium.org/1146923005

R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/1168623002

This also fixes a bug that was preventing markNeedsLayout from working

R=abarth@chromium.org, eseidel@chromium.org, abarth, eseidel

Review URL: https://codereview.chromium.org/1160013004

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1166773003

We'll eventually turn this into a full fn2 component, but for now it's just an
example.

To make this work, I created a schedule.dart as a start to implementing
scheduler.md. For now, I've kept the API similar to the web platform so that
the old world can continue use it backed by sky.window.requestAnimationFrame.

R=eseidel@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1145973009

Experimenting with using the observatory profiler, I noticed two pieces of
low-hanging performance fruit. This change removes about 4% of the total
profile for layouting out and painting the flex demo.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1155043004

Previously layout2.dart was a thousand lines long.

R=ianh@google.com

Review URL: https://codereview.chromium.org/1161003002