One accessibility tree per frame.

chrome/browser/extensions/api/automation/automation_apitest.cc

Index: chrome/browser/extensions/api/automation/automation_apitest.cc
diff --git a/chrome/browser/extensions/api/automation/automation_apitest.cc b/chrome/browser/extensions/api/automation/automation_apitest.cc
index 7bed325470e97f8c305ed5f3aff99149e1c5856c..7eed2f3e12f5ad8739f624b5f490df8ed6b34bad 100644
--- a/chrome/browser/extensions/api/automation/automation_apitest.cc
+++ b/chrome/browser/extensions/api/automation/automation_apitest.cc
@@ -172,6 +172,13 @@ IN_PROC_BROWSER_TEST_F(AutomationApiTest, DesktopFocusWeb) {
       << message_;
 }
 
+IN_PROC_BROWSER_TEST_F(AutomationApiTest, DesktopFocusIframe) {
+  StartEmbeddedTestServer();
+  ASSERT_TRUE(
+      RunExtensionSubtest("automation/tests/desktop", "focus_iframe.html"))
+      << message_;
+}
+
 IN_PROC_BROWSER_TEST_F(AutomationApiTest, DesktopFocusViews) {
   AutomationManagerAura::GetInstance()->Enable(browser()->profile());
   // Trigger the shelf subtree to be computed.