[chromedriver] Add shadow DOM support to chromedriver.

chrome/test/chromedriver/js/focus.js

Index: chrome/test/chromedriver/js/focus.js
diff --git a/chrome/test/chromedriver/js/focus.js b/chrome/test/chromedriver/js/focus.js
index 2945a34c9a74bf93133054d544861467c64432c9..20b48db7a6951b54030d4fe63c15e52e00c07305 100644
--- a/chrome/test/chromedriver/js/focus.js
+++ b/chrome/test/chromedriver/js/focus.js
@@ -38,6 +38,25 @@ function focus(element) {
         throw error;
     }
   }
-  if (element != doc.activeElement)
+
+  var activeElement = doc.activeElement;
+  // If the element is in a shadow DOM, then as far as the document is
+  // concerned, the shadow host is the active element. We need to go through the
+  // tree of shadow DOMs to check that the element we gave focus to is now
+  // active.
+  if (element != activeElement) {
+    var shadowRoot = activeElement.shadowRoot;
+    while (shadowRoot) {
+      var activeElement = shadowRoot.activeElement;
+      if (element == activeElement) {
+        // the shadow DOM's active element is our requested element. We're good.
+        break;
+      }
+      // The shadow DOM's active element isn't our requested element, check to
+      // see if there's a nested shadow DOM.
+      shadowRoot = activeElement.shadowRoot;
+    }
+  }
+  if (element != activeElement)
     throw new Error('cannot focus element');
 }