Initial addition of a11y test dump infrastructure.
This patch adds some basic infrastructure to dump the contents of the platform specific BrowserAccessibility* trees.
A subset of platform specific properties has not yet been added; the BrowserAccessibility::toString() will hold such a representation. For now, every node has it's contents dumped; we can possibly use the "id" html attribute to identify "test" nodes in the future.
The BrowserTreeDumpTest class generates a baseline when one is found and compares it to the live tree resulting from loading html from
chrome/test/data/accessibility.
BUG=none
TEST=none
Review URL: http://codereview.chromium.org/
8971006
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@115418 0039d316-1c4b-4281-b951-d872f2087c98