mock file system
implement a test
Include all required CSS dependencies from spark.css, not spark.html
fix double click on folder; speed up app launch
Merge pull request #229 from dart-lang/files-mock-2

Files mock 2
Merge pull request #251 from dart-lang/double-click-folder

fix double click on folder; speed up app launch
Merge pull request #238 from ussuri/single-css-entry

Include all required CSS dependencies from spark.css, not spark.html
Merged