Enable DumpAccessibilityTree tests to use cross-process iframes.

content/browser/accessibility/accessibility_tree_formatter_mac.mm

Index: content/browser/accessibility/accessibility_tree_formatter_mac.mm
diff --git a/content/browser/accessibility/accessibility_tree_formatter_mac.mm b/content/browser/accessibility/accessibility_tree_formatter_mac.mm
index 88f7978c54ae3d2e26000c20c02063bd2ce77c46..2b2e57074f6c403fe5ea8d01cab858ecd2f0b126 100644
--- a/content/browser/accessibility/accessibility_tree_formatter_mac.mm
+++ b/content/browser/accessibility/accessibility_tree_formatter_mac.mm
@@ -41,7 +41,7 @@ scoped_ptr<base::DictionaryValue> PopulatePosition(
   // based on the lower-left corner of the object. To make this easier and less
   // confusing, convert it to local window coordinates using the top-left
   // corner when dumping the position.
-  BrowserAccessibility* root = node.manager()->GetRoot();
+  BrowserAccessibility* root = node.manager()->GetRootManager()->GetRoot();
   BrowserAccessibilityCocoa* cocoa_root = root->ToBrowserAccessibilityCocoa();
   NSPoint root_position = [[cocoa_root position] pointValue];
   NSSize root_size = [[cocoa_root size] sizeValue];