Now you can use --snapshot to load snapshots from the command line and have
them appear visually on Mac. Also, remove code duplication with Linux by
factoring common testing code into //sky/shell/testing.

Looks like the Keyboard service is only for iOS. We shouldn't try to build it
on Mac.

For some reason having |packages| in this .gitignore file is causing Atom to
grey out all the files in the Sky package. Moving the entry up to the root of
the git repo fixes the issue.

And use the service in mine_digger to notify the user when they flag a bomb.

We need to compute whether a RenderObject has a composited descendant so that
we can decide whether to use canvas.saveLayer or to create a new composited
layer while walking down the tree during painting.

The compositing update walks the tree from the root only to places where the
tree's structure has been mutated. In the common case during an animation loop,
we won't need to visit any render object beyond the root.

This patch makes it easier to debug layerization issues.

We used to do this in the SkPicture, but it's simpler to do it in the
rasterizer now that we're using multiple SkPictures in Dart.

Separating these notions makes them easier to work with because offset is
relative to the parent layer whereas size is intrinsic to the layer itself.
This patch fixes the underpainting bugs when compositing the stocks example.

This generalization will let us implement other alogorithims that need to walk
the RenderObject tree.

Now we have the ability to draw multiple PictureLayers. We still squash all the
pictures together into a single SkPicture for simplicity. In the future, we'll
submit them to C++ separately and composite them on the GPU thread.

Setting a ProgressIndicator's value to null (the default) makes it an "indeterminate progress" or activity indicator.

The indeterminate animations for both kinds of progress bars are essentially the same and wrong vis the Material Design spec, http://www.google.com/design/spec/components/progress-activity.html. I'll improve conformity with the visual design in a future CL.

Used for AnimationPerformance with a single AnimatedValue<T> variable.

Currently we have a single PictureLayer that everyone draws into. A future
patch will teach the system to use multiple PictureLayers.

traces from base and the shell view dart isolate simultaneously.
Trace files contain samples from multiple sources and must be merged
separately

This patch prepares for introducing the compositing system by repurposing the
relevant parts of the createsNewDisplayList system. This patch also removes the
no-longer-relevant parts of that system.

http://developer.android.com/reference/android/view/View.html#onCheckIsTextEditor()
says that we should return true if the "primary purpose" of
the view is text editing.  The keyboard still seems to work
fine if we return false here (default implementation) so
I'm removing this for now.

Fixes https://github.com/domokit/sky_engine/issues/116

@abarth

We seem to have trouble killing sky_server by its pid. Instead, lets try
killing it by looking up which process is listening on the sky_server port.

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

1. We would assert if you tried to start an animation from within an
animation status callback. This is a common pattern, so I fixed this
assert (in Ticker._tick).
2. We would assert for animations with duration under a millisecond.
Fixed.

Also removed the workarounds assocated with #1.

Instead of appending the first path component, we should use it to initialize
`result`. That makes this code work with absolute paths.

We could update all our other versions as well if we wanted
but this the only package in sky which uses sdk_ext

@abarth

Previously we were doing the bounds testing for hit tests in the parent, but
that doesn't work if the child paints at a location other than 0.0, 0.0. Now we
do the bounds check in the child. This also simplifies Scaffold's hit testing.

Fixes #558

Instead we use the packages directory which is at the same
level as the BUILD.gn file.  That's a bit of a broken assumption
but it happens to work for all our skyx uses for now.

@abarth

@abarth @collinjackson