Mention typedefs in the sky dart style guide.

sky/specs/style-guide.md

 Sky Style Guide
 ===============
 
 In general, follow our [Design Principles](design.md) for all code.
 
 
 Dart
 ----
 
 In general, follow the [Dart style
 guide](https://www.dartlang.org/articles/style-guide/) for Dart code,
 except where that would contradict this page.
 
 Always use the Dart Analyzer. Do not check in code that increases the
 output of the analyzer unless you've filed a bug with the Dart team.
 
 Use assert()s liberally.
 
 
-Classes and Enums are named UpperCamelCase. Everything else (methods,
-fields, variables, constants, enum values, etc) is lowerCamelCase.
-Global double and string constants are prefixed with k. Prefer using a
-static const in a relevant class than using a global constant.
+Types (i.e. classes, typedefs (function signature definitions) and
+enums) are named UpperCamelCase. Everything else (methods, fields,
+variables, constants, enum values, etc) is lowerCamelCase. Global
+double and string constants are prefixed with k. Prefer using a static
+const in a relevant class than using a global constant.
 
 Don't name your libraries (no ```library``` keyword). Name the files
 in ```lower_under_score.dart``` format.
 
 
 Class constructors and methods should be ordered in the order that
 their members will be used in an instance's typical lifecycle. In
 particular, this means constructors all come first in class
 declarations.
 
@@ skipping 62 matching lines @@
 > ```
 
 
 C++
 ---
 
 
 Java
 ----