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This is a prerequisite for adding file handling on Windows, MacOS and
Linux.

Example:
./chrome --profile-directory=my-profile --app-id=.. -- -- file1 file2 file3

Note: In future, the FileHandlerManager will infer the correct FileHandler for
an app based on the files it is given. For now, it just opens the app's launch
url.

Bug: 938103
Change-Id: Ieaa136d109fc906c9c48a95cdbd194fb0622d3cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1819286Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Jay Harris <harrisjay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702740}