[Native File System] Keep track of frame for each handle.

In preparation for implementing permission prompts we'll need to keep
track of which frame any particular handle is associated with. Also
adds a common base class to the file/directory handle implementations,
as there is going to be more functionality shared between the two.

Bug: 878585
Change-Id: I07cd8273f1ae41a8f1eb95fc7d8fbfeb3311cf72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1625809
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Auto-Submit: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664349}
12 files changed