NOTE: This CL appears far larger than it actually is for two reasons:

1) Many files were moved around to use the Dart package directory structure.
2) Many .dart files had to have import paths updated.

- Organize mojo/public/dart so that it uses standard Dart package layout
- Organize mojo/dart/apptest so that it uses a standard Dart package layout
- Organize sky/sdk so that it uses a standard Dart package layout
- Create a mojo/testing package (used by unittests)
- Introduce the 'dart_pkg' gn rule which populates gen/Config/dart-pkg
- All internally vended Dart packages must have a corresponding dart_pkg rule
- It is now possible to use dependency_overrides: in pubspec.yaml to mix internal and external package dependencies (enables analyzer, editor, webstorm usage for internal developers).
- Package root for dart content handler ends with "packages/"
- Imports of mojo package uris no longer need the "public/dart"
- mojo/public/tools/dart_package.py is a clone of mojo/public/tools/gn/zip.py
- Sky tests no longer run 'deploy_sdk' script.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1132063007

[Effen] Port fn.dart from the legacy sky.Node backend to the RenderNode backend, which is currently just a sky.Node-backed shim, but will eventually be the core Sky interface for layout and painting.

- the custom layout class in fn is removed by this patch; a new class
  will be added in a later CL

- the version of layout.dart in this CL is a subset of what we're
  targetting on the long run with
     https://codereview.chromium.org/1093633002

- a couple of lines of dead code are removed in this CL also

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1117143003

Analyzer was complaining about '-' not being an allowed character
in dart file names.

R=jamesr@chromium.org

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1104233003

TBR=eseidel

Review URL: https://codereview.chromium.org/1065643003

TBR=eseidel

Review URL: https://codereview.chromium.org/1066513006

Pipe the remaining time for an animation all the way out to the AnimatedValue.
Make splashes abortable, which causes them to continue to fade but no longer grow, by having them fade in 100ms or however long the animation was still going to go for, whichever is quickest.
Make Scrollables support objects registering with them to be told when scrolling happens.
Make UINode support subclasses being informed when _remove() was called.
Hook all that together to make splashes go away when scrolling by having them register with any ancestor Scrollables such that when those scroll, all the splashes get aborted. Unregister when removed.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1092423003

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1043283003

1) Factors InkWell out of Material so that components can use an ink well
   without needing the shadow/level machinery.

2) Makes the ink effect move at a different velocity once the tap has actually
   occurred, converging with the spec. We don't have the right speeds yet, but
   at least we're approaching the right shape.

3) To support (2), added a primaryPointer attribute to GestureEvents to let
   authors coorelate gesturetapdown events with later gesturetap events.

4) To support (2), modernized SplashAnimation to used AnimatedValue and friends.

5) Added more constants to view-configuration.dart that match Android.

I've also removed the cancelling of the ink effect on scroll. The proper way to
do that is to notice that someone in the event chain is listening for
scrollstart and delay the beginning of the ink effect for some period of time.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1019023003

This CL is a warmup for using a more sophisticated gesture disambiguation.

1) Use gesturetap instead of click. We should probably remove click events
   because folks should use gesturetap to integrate with the gesture system.

2) Handle the case where you swipe the drawer during an animation. Previously
   we had an assert which triggered in some multitouch scenarios. We'll
   eventually move this over to gestureswipe.

3) Remove an extra container for ink splashes. There's no need to group all the
   ink splashes in a container. They can all just be children of the Material
   component itself. This structure is left over from when Material was a base
   class.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1013713005

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1006053002

This CL cleans up the sky/framework/animation as follows:

1) I've moved code that's used only by the custom elements framework into
   sky/framework/elements/animation. This code is based on AnimationDelegates
   rather than Streams.
2) Rename ScrollCurve to ScrollBehavior because it encapsulates more behavior
   than just a curve.
3) Make the Generator interface explicit and mark subclasses as actual
   subclasses.
4) Move Simulation into generators.dart because it implements the Generator
   interface.
5) Move Animation out of generators.dart because it does not implement the
   Generator interface.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1001373002

This CL teaches Scrollable how to settle back to a scroll offset of 0.0 after a
fling or a scroll. There's still some room for improvement:

1) Some of this logic should be factored out into the scroll curve object.
2) We don't produce the correct animation curves when we fling into the
   overscroll region because we wait for the fling velocity to reach zero
   before we start the settling animation.

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

Review URL: https://codereview.chromium.org/1005753002

To accomplish this, I made the following changes:

1) Material is now in charge of drawing the material shadows.
2) In order to mix in the style for the shadow, Element now takes a list of
   Styles instead of a single style.
3) Update all clients of Element#style to understand that we now have a list.
4) Update components that drawer shadows to have Material do that work instead.
   a) One exception: FloatingActionButton draws its own shadow because of its
      crazy clip requirements. We'll probably want to find a better way for
      FloatingActionButton to clip in the future.

I've also added a widgets-fn example to demo the fn material widgets.

This CL introduces a bug into Drawer whereby you can get ink splashes
everywhere in the drawer. In the future, we'll need to separate out the
different material aspects to get non-splashable materials.

R=rafaelw@chromium.org

Review URL: https://codereview.chromium.org/1003553002

Moving these files into sky/framework will make them easier to use from the
SDK. Also, this CL also splits up the giant "widgets" library into smaller
libraries, one per component.

TBR=eseidel@chromium.org

Review URL: https://codereview.chromium.org/993033003

"Render" is misleading. "Build" may not be the best word either, it's closer to what's actually happening.

R=ojan@chromium.org
TBR=abarth
BUG=

Review URL: https://codereview.chromium.org/992033002

This is just a proof of concept. If we like this direction, it will move out of the examples directory (likely re-written) and be committed in smaller pieces with unit tests and formal reviews.

TBR=abarth
BUG=

Review URL: https://codereview.chromium.org/971183002