Add support for text styles - Work In Progress

Add support for text styles - Work In Progress

Added a TextStyle class and a style: parameter in Text, Paragraph. The stock app uses it to make the Toolbar's
title white.

I haven't been able to finish converting the info in typography.dart to TextStyle objects. The final fields
in _Black don't compile because the fontSize:,fontWeight:
parameter values aren't const. 


Closes #213

[Hixie, 2015-06-11 17:39:26]

ianh@google.com changed reviewers:
+ ianh@google.com

[Hixie, 2015-06-11 17:39:28]

This approach seems sound.

https://codereview.chromium.org/1176133002/diff/1/sky/sdk/lib/framework/rende...
File sky/sdk/lib/framework/rendering/paragraph.dart (right):

https://codereview.chromium.org/1176133002/diff/1/sky/sdk/lib/framework/rende...
sky/sdk/lib/framework/rendering/paragraph.dart:15: final Color color;
constructor then fields (see sky/specs/style-guide.md)

https://codereview.chromium.org/1176133002/diff/1/sky/sdk/lib/framework/rende...
sky/sdk/lib/framework/rendering/paragraph.dart:16: final String fontSize;
fontSize should be a double (pixels).

https://codereview.chromium.org/1176133002/diff/1/sky/sdk/lib/framework/rende...
sky/sdk/lib/framework/rendering/paragraph.dart:17: final String fontWeight;
fontWeight should be an enum.

https://codereview.chromium.org/1176133002/diff/1/sky/sdk/lib/framework/rende...
sky/sdk/lib/framework/rendering/paragraph.dart:25: bool operator ==(other) =>
other is TextStyle &&
If you have an operator ==, you need a hashCode function.

Also, only use => if it fits on one line.

[eseidel, 2015-06-12 00:22:15]

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

[eseidel, 2015-06-12 00:22:15]

Picked up this patch and finished it in
https://codereview.chromium.org/1178913003.