Clean up extensions permissions unit tests
* Move socket_permission_unittest.cc and usb_device_permission_unittest.cc
into src/extensions -- they have no src/chrome dependencies.
* Move permissions_data_unittest.cc back into src/chrome -- its tests rely on
extension manifest keys that aren't part of src/extensions yet.
* Rename the latter tests to PermissionsDataTest
BUG=397165
TEST=unit_tests PermissionsDataTest.* and extensions_unittests
Review URL: https://codereview.chromium.org/
563663002
Cr-Commit-Position: refs/heads/master@{#294493}