Prototype of fn3

We were just missing a few type casts in tests to make the analyzer happy.

This patch contains a prototype of a new widget framework. In this framework,
Components can be reused in the tree as many times as the author desires. Also,
StatefulComponent is split into two pieces, a ComponentConfiguration and a
ComponentState. The ComponentConfiguration is created by the author and can be
reused as many times as desired. When mounted into the tree, the
ComponentConfiguration creates a ComponentState to hold the state for the
component. The state remains in the tree and cannot be reused.

Instead of having to manage the popup menu from your app's build
function, you now just call showPopupMenu() with the menu's position and
it takes care of everything for you.

This solves the problem that the popup menu was trying to mutate the
state of the navigator from within its own initState() function.

Also, remove the "route" argument to RouteBase.build() since it equals
"this" by definition...

Also, remove ModalOverlay, and instead put that logic in the navigator.

Improvements to EffectLine in sprites

Move findAncestorRenderObjectWrapper to RenderObjectWrapper

Fix Rect intersection; add test

That way it's closer to where it's used, and it's more obvious that
anyone can write such functions.

- Fix AnimationTiming to have defaults for 'interval' and 'curve' since
  that seems to be how we use it.

- Merge RouteBase.build and RouteBase.buildTransition

- Get rid of HistoryEntry, since it added nothing

- Broke out RouteBase.createPerformance() so subclasses can change what
  is created.

- Build the routes backwards so that we more efficiently avoid building
  hidden routes.

- Introduce an explicit way (!hasContent) for RouteState to avoid
  building, rather than the implicit "build returns null" we had before.

In EditableText, wrap the placeholder text in a Row so it will expand to its parent's width

This will ensure that the width of an empty Input is consistent with the
width of an Input that contains text.

Also add a unit test for the Input widget and a way for tests to provide mock
implementations of Mojo services such as the keyboard.

SkySprites should import the public libraries

Require that you pass transitions a performance.

Importing the public libraries caused a name conflict with dart:sky because we
assume people will import dart:sky into a namespace, so I've also changed
skysprites to import dart:sky into a namespace.

I've also removed the top-level description of the Sky package. Instead, we
should host that content on flutter.io.

This fixes #1103.

This might be helpful for #1219.

Also, remove inDebugMode since it's redundant with just using asserts,
which compile entirely out in release mode.

Also, introduce Colors and Typography to hold the material colors and the
typography declarations. Previously we expected clients of these libraries to
import them into a namespace, but that doesn't play nice with re-exporting them
from material.dart.

When we sync() a Component, we need to clear the old Component's _child
pointer, otherwise if we reuse that Component we'll get confused about
what the old child is.

Improve debugging aids for widgets, rendering.

Kill the sky_server on Mac in a way that works to avoid unexpected behavior when working with more than one app at once.

Remove the skyx package

This code is now part of sky_tools.

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.

Adds TexturedLine and animated EffectLine to sprites

We were not removing children if they were more recently synced than we
were. This makes no sense. We should remove all children unless they
were synced this very generation already (in which case they'll be
somewhere else in the tree by now).

We removed this value from the engine because it's not useful.

What's important about this code is that it's presenting services outside the
VM, not the particular technology used to present the services.

This patch is part of a sequence of patches towards fewer top-level libraries.
In this patch, the gesture libraries are combined into one gestures.dart
library.

Conflicts:
	examples/widgets/scale.dart

First pass at support for pinch gestures; panning issues (needs testing)

Conflicts:
	sky/packages/sky/lib/gestures/drag.dart