Using Flash Builder 4.6, Flex 4.6.0, AIR 3.5. If you get errors where the flash.data package cannot be imported, it suggests you have not included the AIR files in your project. In Flash Builder, when configuring your project when you create it, you must check the extra checkbox in the area near your Flex API selection for *Include Adobe AIR libraries*, or alternatively, after setting up your project, you can edit the project > Flex Library Compiler pane, at the top in the Flex SDK version configuration area you can check the *Include Adobe AIR libraries*.
Also, you may need to include the defaults.css file in the library manually:
Properties >> Flex Library Build Path >> Assets tab >> unfurl the src folder and check the box next to defaults.css.