Split Size into Size and Offset.

Split Size into Size and Offset.

Added a OffsetBase class that Size now inherits from, and added a new
Offset class that also inherits from OffsetBase.

Offset has:
 - dx and dy members
 - zero and infinite static constants
 - a method that returns a new Offset that's the existing one scaled
   by a scalar
 - a unary minus operator
 - operators overloads such that subtracting or adding two Offsets
   gives another Offset
 - a toPoint() method

Added Offset and Size to the dart bindings, so they can be used from C++.

Changed the Canvas API to use Point, Size, and Offset where appropriate:
 - drawLine uses Points now
 - drawCircle uses a Point now
 - drawImage uses a Paint now
 - the constructor uses a Size

Changed Point as follows:
 - added a unary minus
 - Point difference now gives an Offset rather than a Size
 - You can add an Offset to a Point to get a new Point
 - toSize() has been replaced by toOffset()

Changed Rect as follows:
 - renamed upperLeft and lowerRight to topLeft and bottomRight for
   consistency with our other APIs
 - added bottomLeft and topRight for completeness

Changed Size as follows:
 - now inherits from OffsetBase
 - added *, /, ~/, and % operators for scaling sizes
 - subtracting a Size from a Size gives an Offset
 - subtracting an Offset from a Size gives a Size
 - changed the + operator to take an Offset instead of a Size
 - added topLeft, bottomLeft, topRight, bottomRight to match Rect
 - added center for the same reason
 - added shortestSide getter since that was a common pattern
 - removed toPoint()

Changed DrawLooperLayerInfo as follows:
 - setOffset member takes an Offset instead of a Point

Changed BoxConstraints as follows:
 - added biggest getter since it was a common pattern
 - added smallest getter for symmetry

Changed BoxShadow as follows:
 - offset member is an Offset rather than a Size

Changed ViewConstraints as follows:
 - replaced height and width members by a single size member

I did some minor code cleanup in nearby files while I was there,
including sorting sky/engine/core/core.gni alphabetically, and fixing
some warnings in the examples.

BUG=
R=abarth@chromium.org, chinmaygarde@google.com

Committed: https://chromium.googlesource.com/external/mojo/+/196833cdb92a7cdada6f60aa95d45a1aa54cf378

[Hixie, 2015-06-26 21:52:43]

ianh@google.com changed reviewers:
+ abarth@chromium.org

[Hixie, 2015-06-26 21:52:43]

(I've found a couple of things that need fixing still but overall it should be
ready for review.)

[Chinmay, 2015-06-26 21:55:18]

chinmaygarde@google.com changed reviewers:
+ chinmaygarde@google.com
- abarth@chromium.org

[Chinmay, 2015-06-26 21:55:18]

lgtm

https://codereview.chromium.org/1214833004/diff/20001/sky/engine/core/paintin...
File sky/engine/core/painting/OffsetBase.dart (right):

https://codereview.chromium.org/1214833004/diff/20001/sky/engine/core/paintin...
sky/engine/core/painting/OffsetBase.dart:23: int result = 373;
Maybe we should move this way of constructing hash codes (this is Josh Bloch
proposed method right?) into a utility method. I always need to look it up when
I override hashCode.

[abarth-chromium, 2015-06-26 22:04:41]

abarth@chromium.org changed reviewers:
+ abarth@chromium.org

[abarth-chromium, 2015-06-26 22:04:43]

lgtm

https://codereview.chromium.org/1214833004/diff/20001/sky/engine/core/paintin...
File sky/engine/core/painting/Offset.dart (right):

https://codereview.chromium.org/1214833004/diff/20001/sky/engine/core/paintin...
sky/engine/core/painting/Offset.dart:25: // does the equivalent of "return new
Point(0,0) + this"
s/new Point(0,0)/Point.origin/

https://codereview.chromium.org/1214833004/diff/20001/sky/engine/core/paintin...
File sky/engine/core/painting/Size.dart (right):

https://codereview.chromium.org/1214833004/diff/20001/sky/engine/core/paintin...
sky/engine/core/painting/Size.dart:39: Size get square {
inscribedSquare?

Another square is the boundingSquare...

[Hixie, 2015-06-26 22:21:33]

Committed patchset #4 (id:60001) manually as
196833cdb92a7cdada6f60aa95d45a1aa54cf378 (presubmit successful).