Added win7 specific expected file.

CL 1893118 introduced a new dump test that uses PosInSet/SizeOfSet,
which are not available on Win7's UIA implementation. This change
adds an expected file for Win7 that does not include these properties

Original CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1893118


Change-Id: I2d6b43a67b18e30dd864e46f83479b5819e9e5d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1906927Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Kevin Babbitt <kbabbitt@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#713935}

content/test/data/accessibility/aria/aria-tree-discontinuous-expected-uia-win7.txt

+document
+++tree Selection.CanSelectMultiple=false Selection.IsSelectionRequired=false
+++++treeitem Name='card content' ExpandCollapse.ExpandCollapseState='LeafNode' SelectionItem.IsSelected=false
+++++group
+++++treeitem Name='card content' ExpandCollapse.ExpandCollapseState='LeafNode' SelectionItem.IsSelected=false
\ No newline at end of file