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This CL is part of the work on file-handling:
https://github.com/WICG/file-handling/blob/master/explainer.md

After this CL, websites will be able to access files (if any) that
they were launched with.

This feature is hidden behind two experimental flags:
NativeFileSystemAPI and FileHandlingAPI.

Bug: 829689
Change-Id: I503afebb7d5ee00eff3bc032245c57966ca34872
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1672608
Commit-Queue: Jay Harris <harrisjay@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680279}