fix(mdTooltip): Tooltip role (#10052)

The tooltip role was being assigned to an element that is being
detached and not re-attached, causing an a11y issue. The tooltip
role is now being assigned to the panel element through the `role`
attribute.

Fixes #10045

Author: bradrich

src/components/tooltip/tooltip.js

@@ -89,7 +89,6 @@ function MdTooltipDirective($timeout, $window, $$rAF, $document, $interpolate,
 
     // Remove the element from its current DOM position.
     element.detach();
-    element.attr('role', 'tooltip');
 
     updatePosition();
     bindEvents();
@@ -385,7 +384,9 @@ function MdTooltipDirective($timeout, $window, $$rAF, $document, $interpolate,
         panelRef = $mdPanel.create(panelConfig);
       }
 
-      panelRef.open();
+      panelRef.open().then(function() {
+        panelRef.panelEl.attr('role', 'tooltip');
+      });
     }
 
     function hideTooltip() {