Expose internal treegrid role, do some cleanup for table/grid/treegrid handling

chrome/test/data/extensions/api_test/automation/tests/tabs/attributes.js

Index: chrome/test/data/extensions/api_test/automation/tests/tabs/attributes.js
diff --git a/chrome/test/data/extensions/api_test/automation/tests/tabs/attributes.js b/chrome/test/data/extensions/api_test/automation/tests/tabs/attributes.js
index 92f65aeb245550f42910047217b80e82eb837f48..75cdaf592a4046c6862c230d25f9a37d10bca7a9 100644
--- a/chrome/test/data/extensions/api_test/automation/tests/tabs/attributes.js
+++ b/chrome/test/data/extensions/api_test/automation/tests/tabs/attributes.js
@@ -168,7 +168,7 @@ var allTests = [
   },
 
   function testTableAttributes() {
-    var table = rootNode.find({ role: 'table' });;
+    var table = rootNode.find({ role: 'grid' });;
     assertEq(3, table.tableRowCount);
     assertEq(3, table.tableColumnCount);