unittests: Replace setfattr command with its C++ version.

This patch replaces a call to EXPECT_COMMAND with the C++ version
of the same, implemented in the function SetExpectedFileSize().

BUG=chromium:289444
TEST=unittests (including disabled).

Change-Id: Ief6696ffbf3cf21561410a63e51e17db050aa0b2
Reviewed-on: https://chromium-review.googlesource.com/169010
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
4 files changed