canvasevent: dont pass identity transform

[milahu]

benefit: make snapshots smaller

[jtenner]

Believe it or not this impacts cpu performance, probably causing v8 to have a harder time optimizing this function. Considering it will be a high traffic function and this would be considered a micro-optimization, I would request some speed metrics to validate the "if" branch is actually faster.

[milahu]

Believe it or not this impacts cpu performance

yes i believe that ; ) good old space-time-tradeoff

to solve the problem at its root:
we could keep track of the ctx._transformStack
and make getTransformSlice return undefined
if the current transform is the identity transform
( canvas._transformIsIdentic == true )
so that createCanvasEvent can omit the transform field

replay the recorded API calls - this should be a separate issue

for my app, it would be ideal to save the capture as JS code, like

// var c = document.createElement('canvas')
// var x = c.getContext('2d')
x.drawFoo()
x.drawBar()
  var p = new Path2D()
  p.drawSome()
  p.drawThing()
    var p1 = new Path2D()
    p1.drawAnother()
    p1.drawThing()
  p.addPath(p1)
x.addPath(p)
// ....

then the consumer can simply call eval('x.drawFoo()')

or encapsulate/compile frames into functions
like var f = new Function('x', 'x.drawFoo()') and call f(ctx)

edit: i dont need prop-objects like { x: 1, y: 2, foo: "three", bar: null }
and im happy with positional argument arrays like [ 1, 2, "three", null ]
= less overhead for most consumers

[milahu]

closing for #77