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

Files mock 2
Merged
Simplified code. Fixed the merge.
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
Fixed nits
Merged
Fixed merge
Merge pull request #254 from dinhviethoa/250-alt-for-new-tab

Implemented Alt to open a new tab (fixed #250)
add context menu ux; merge to master