fix(aria): $mdAria should not use texts from aria-hidden nodes

* $mdAria is currently just using `textContent` for retrieving the `aria-label`.
  This is not valid, since some child-texts can be hidden in aria (`aria-hidden="true")

* Using a TreeWalker is super elegant and performant.
  The current use of the TreeWalker is supported by all browser we support.

Fixes #7376

Closes #7957

src/core/services/aria/aria.js

@@ -50,7 +50,7 @@ function AriaService($$rAF, $log, $window, $interpolate) {
 
   function expectWithText(element, attrName) {
     var content = getText(element) || "";
-    var hasBinding = content.indexOf($interpolate.startSymbol())>-1;
+    var hasBinding = content.indexOf($interpolate.startSymbol()) > -1;
 
     if ( hasBinding ) {
       expectAsync(element, attrName, function() {
@@ -62,7 +62,26 @@ function AriaService($$rAF, $log, $window, $interpolate) {
   }
 
   function getText(element) {
-    return (element.text() || "").trim();
+    element = element[0] || element;
+    var walker = document.createTreeWalker(element, NodeFilter.SHOW_TEXT, null, false);
+    var text = '';
+
+    var node;
+    while (node = walker.nextNode()) {
+      if (!isAriaHiddenNode(node)) {
+        text += node.textContent;
+      }
+    }
+
+    return text.trim() || '';
+
+    function isAriaHiddenNode(node) {
+      while (node.parentNode && (node = node.parentNode) !== element) {
+        if (node.getAttribute && node.getAttribute('aria-hidden') === 'true') {
+          return true;
+        }
+      }
+    }
   }
 
   function childHasAttribute(node, attrName) {
@@ -74,17 +93,18 @@ function AriaService($$rAF, $log, $window, $interpolate) {
       return (style.display === 'none');
     }
 
-    if(hasChildren) {
+    if (hasChildren) {
       var children = node.childNodes;
-      for(var i=0; i<children.length; i++){
+      for (var i=0; i < children.length; i++) {
         var child = children[i];
-        if(child.nodeType === 1 && child.hasAttribute(attrName)) {
-          if(!isHidden(child)){
+        if (child.nodeType === 1 && child.hasAttribute(attrName)) {
+          if (!isHidden(child)) {
             hasAttr = true;
           }
         }
       }
     }
+
     return hasAttr;
   }
 }

src/core/services/aria/aria.spec.js

@@ -60,6 +60,37 @@ describe('$mdAria service', function() {
       button.remove();
 
     }));
+
+    it('should correctly retrieve the aria-label text', inject(function($compile, $rootScope, $mdAria) {
+      var container = $compile(
+        '<div>' +
+          'PLAIN' +
+          '<span>SPAN</span>' +
+          '<div>DIV</div>' +
+        '</div>'
+      )($rootScope);
+
+      $mdAria.expectWithText(container, 'aria-label');
+
+      expect(container[0].textContent).toBe('PLAINSPANDIV');
+      expect(container.attr('aria-label')).toBe('PLAINSPANDIV');
+    }));
+
+    it('should ignore aria-hidden texts when retrieving aria-label', inject(function($compile, $rootScope, $mdAria) {
+      var container = $compile(
+        '<div>' +
+          'PLAIN' +
+          '<span aria-hidden="true">SPAN</span>' +
+          '<div aria-hidden="true">DIV</div>' +
+        '</div>'
+      )($rootScope);
+
+      $mdAria.expectWithText(container, 'aria-label');
+
+      expect(container[0].textContent).toBe('PLAINSPANDIV');
+      expect(container.attr('aria-label')).toBe('PLAIN');
+    }));
+
   });
 
 });