Implement "preserving last modified" for Copy() and Move() on cross file system.

This CL implements "preserving last modified" feature for Copy() and Move() on
cross file system. As specification says, the failing of TouchFile shouldn't be
an error, so errors are just ignored.

BUG=282107
TEST=Ran unit_tests and content_unittests

Review URL: https://codereview.chromium.org/24593002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225504 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225504
cc: Add shared quad states correctly in unit tests.

When we add quads for tests we must do so in a valid way. We were
adding quads for the same SharedQuadState with quads for a different
SharedQuadState in between, but that's totally uncool.

Add a third SharedQuadState so that quads refer to SharedQuadStates
in a contiguous way as we would like in reality.

R=piman
BUG=263069

Review URL: https://codereview.chromium.org/24596005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225505 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225505