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This function has historically been opening a file for exclusive r/w/d
with FILE_ALL_ACCESS. FILE_ALL_ACCESS is nearly almost never, ever the
right choice when opening a file. This is especially true when opening a
file from an ordinary non-elevated user session, since it attempts to
gain things like WRITE_DAC and WRITE_OWNER and will fail if it's not
possible to gain those access rights.

A better way to determine if a file is "in use" (and what we really mean
is "is an executable that is running") is simply to try to write to
it. This is because CreateProcess opens its target with only exclusive
write mode (read and execute are shared for obvious reasons).

This change also eliminates the exact copy of this function, which
included the incorrect formatting from the original, that was used in
the unittest.

R=gab@chromium.org

BUG: 474401
Change-Id: I0488e2a5333f74353f46ae6c87795e2833a30b61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1905948
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Reviewed-by: David Bienvenu <davidbienvenu@chromium.org>
Auto-Submit: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713858}