Add support for transforms to container

Add support for transforms to container

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

R=eseidel@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/b9b6d821a10719a6ae39a8dfc5b1feb9653080a2

[eseidel, 2015-06-03 17:16:18]

lgtm

https://codereview.chromium.org/1152273004/diff/1/sky/sdk/lib/framework/rende...
File sky/sdk/lib/framework/rendering/box.dart (right):

https://codereview.chromium.org/1152273004/diff/1/sky/sdk/lib/framework/rende...
sky/sdk/lib/framework/rendering/box.dart:324: void translate(x, [double y=0.0,
double z=0.0]) {
Does the style put a space around these or not?

[abarth-chromium, 2015-06-03 17:20:38]

Committed patchset #1 (id:1) manually as
b9b6d821a10719a6ae39a8dfc5b1feb9653080a2 (presubmit successful).

[Matt Perry, 2015-06-03 17:32:30]

I was planning on exposing some of the SkMatrix operations in the painting API.
Would that let you drop the dependency on vector_math.dart?

[abarth-chromium, 2015-06-03 19:35:56]

On 2015/06/03 at 17:32:30, mpcomplete wrote:
> I was planning on exposing some of the SkMatrix operations in the painting
API. Would that let you drop the dependency on vector_math.dart?

Unfortunately, I don't that will work everywhere.  There are two competing sets
of requirements:

1) Fast matrix manipulations inside the VM for things like hit testing and
physics engines.
2) Fast drawing operations using matrices.

Using Matrix4 everywhere optimizes for (1).  Using an SkMatrix interface
everywhere optimizes for (2).  Because both are important, we'll need some sort
of hybrid approach where some code uses Matrix4 for in-VM manipulation and some
code uses an SkMatrix interface for painting.  My guess is that RenderTransform
is where the two matrix types will come in contact because the clients of
RenderTransform want to talk in Matrix4, RenderTransform needs to do some
operations with Matrix4, but RenderTransform also needs to talk to Canvas using
SkMatrix.