This is the book Dart: Up and Running by Kathy Walrath and Seth Ladd. More info: http://shop.oreilly.com/product/0636920025719.do
The text and code in this repo are old.
The latest text is in the dart-lang/site-www repo under /src/_guides/language/language-tour and /src/_guides/libraries/library-tour.
To see the generated version of these docs, see the Language Tour and Library Tour on dartlang.org.
The latest code is under dart-lang/site-www/tree/master/examples.