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.

These are now called Block, Stack, and Flex, respectively. Less verbose.

R=jackson@google.com, ianh@google.com

Review URL: https://codereview.chromium.org/1181533002.

Also change SizedBox.

This makes the code that uses Container() and SizedBox() much more readable.

The underlying RenderSizedBox is not affected by this change.

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

Review URL: https://codereview.chromium.org/1166203002

TBR=ianh@google.com

Review URL: https://codereview.chromium.org/1164073002

This CL makes gesture events work again in fn2.

R=ianh@google.com

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

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

Also add operator==, hashCode, toString, and some basic Color constants to
Color.

R=abarth@chromium.org, ianh@google.com

Review URL: https://codereview.chromium.org/1162023004

These transforms are currently very basic but they seem to mostly work.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1152273004

This CL is a first pass at implementing container in fn2. In this approach,
Container is a Component that builds a number of RenderNodeWrappers depending
on what is needed.

R=ianh@google.com

Review URL: https://codereview.chromium.org/1158983005

BlockContainer uses a RenderBlock to lay out its children.

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

Review URL: https://codereview.chromium.org/1166473005

Prevously we listened for events on the document and then walked up the
component hierarchy looking for EventListenerNodes. Now we do something similar
by hooking the event dispatching logic in the AppView.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1153343004