Return full relative paths in ListFilesRecursive
Return full relative paths in ListFilesRecursive

ListFilesRecursive was only returning filenames, not the full relative
path from the root directory.

Bug: 182165266
Change-Id: I3d087c39e84e85ce064fd65a7eca7a830ddf9a6d
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto