Inherit Presentation role only when elements without a explicit role defined.

LayoutTests/accessibility/listitem-presentation-inherited.html

+<script src="../resources/js-test.js"></script>
+<ul role="presentation">
+<li role="listitem">Item 1</li>

[dmazzoni, 2015/01/15 16:05:30]

nit: could you indent the <li> elements inside the <ul> to make this easier to
read?

+<li role="listitem">Item 2</li>
+<li role="listitem">Item 3</li>
+</ul>
+
+<ul role="presentation">
+<li>Plain Text 1</li>
+<li>Plain Text 2</li>
+<li>Plain Text 3</li>
+</ul>
+<p>End of test</p>
+<p id="description"></p>
+<div id="console"></div>
+<script>
+description("This tests that the presentation role is inherited.");
+
+if (window.testRunner)
+    testRunner.dumpAsText();
+
+function buildAccessibilityTree(accessibilityObject, indent) {
+    var str = "";
+    for (var i = 0; i < indent; i++)
+       str += "    ";
+    str += accessibilityObject.role;
+    str += " " + accessibilityObject.stringValue;
+
+    if (accessibilityObject.role == '')
+        str += accessibilityObject.allAttributes();
+
+    str += "\n";
+    document.getElementById("console").innerText += str;
+
+    if (accessibilityObject.stringValue.indexOf('End of test') >= 0)
+        return false;
+
+    var count = accessibilityObject.childrenCount;
+    for (var i = 0; i < count; ++i) {
+        if (!buildAccessibilityTree(accessibilityObject.childAtIndex(i), indent + 1))
+            return false;
+    }
+
+    return true;
+}
+
+if (window.accessibilityController) {
+    var body = accessibilityController.focusedElement;
+    buildAccessibilityTree(body, 0);
+}
+</script>