Adds browsertest that ensures that on Win a focus event always fires when...

Adds browsertest that ensures that on Win a focus event always fires when navigating to another page

If a user of Jaws or NVDA screen reader navigates to another page,
they expect their screen reader focus to move to the web contents, otherwise
they might develop the mistaken belief that the virtual buffer hasn't loaded.
I wasn't able to add a DumpEventTest under content/test/data/accessibility/events
because we filter out all focus events and adding them back would cause too many other tests to fail randomly.
This Windows specific browser is my best shot at testing this expectation.

R=dmazzoni@chromium.org, kbabbitt@microsoft.com

Bug: 1058959
Change-Id: I161ea42c38220d5245b68d271af74f8b748b95ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2097389Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749195}

content/browser/accessibility/accessibility_win_browsertest.cc

@@ -48,6 +48,7 @@
 #include "third_party/iaccessible2/ia2_api_all.h"
 #include "third_party/isimpledom/ISimpleDOMNode.h"
 #include "ui/accessibility/accessibility_switches.h"
+#include "ui/accessibility/ax_event_generator.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_tree_host.h"
 
@@ -907,10 +908,42 @@ class WebContentsUIAParentNavigationInDestroyedWatcher
 
 }  // namespace
 
+//
 // Tests ----------------------------------------------------------------------
+//
+
+IN_PROC_BROWSER_TEST_F(AccessibilityWinBrowserTest,
+                       TestAlwaysFireFocusEventAfterNavigationComplete) {
+  ASSERT_TRUE(NavigateToURL(shell(), GURL(url::kAboutBlankURL)));
+
+  // Users of Jaws or NVDA screen readers might not realize that the virtual
+  // buffer has been loaded, if focus hasn't been placed in the document after
+  // navigating to a new page. If a focus event is not received by the screen
+  // reader, it might "think" that focus is outside the web contents.
+  //
+  // We can't use "LoadInitialAccessibilityTreeFromHtml" because it waits for
+  // the "kLoadComplete" event, and the "kFocus" and "kLoadComplete" events are
+  // not guaranteed to be sent in the same order every time, neither do we need
+  // to enforce such an ordering. However, we do need to ensure that at the
+  // point when the "kFocus" event is sent, the document is fully loaded.
+  AccessibilityNotificationWaiter waiter(
+      shell()->web_contents(), ui::kAXModeComplete,
+      ui::AXEventGenerator::Event::FOCUS_CHANGED);
+  GURL html_data_url("data:text/html,<p>Hello world.</p>");
+  ASSERT_TRUE(NavigateToURL(shell(), html_data_url));
+  waiter.WaitForNotification();
+
+  // Check that the page has indeed loaded.
+  AccessibleChecker document_checker(L"", ROLE_SYSTEM_DOCUMENT, L"");
+  AccessibleChecker paragraph_checker(L"", L"P", IA2_ROLE_PARAGRAPH, L"");
+  document_checker.AppendExpectedChild(&paragraph_checker);
+  AccessibleChecker text_checker(L"Hello world.", ROLE_SYSTEM_STATICTEXT, L"");
+  paragraph_checker.AppendExpectedChild(&text_checker);
+  document_checker.CheckAccessible(GetRendererAccessible());
+}
 
 IN_PROC_BROWSER_TEST_F(AccessibilityWinBrowserTest, TestBusyAccessibilityTree) {
-  EXPECT_TRUE(NavigateToURL(shell(), GURL(url::kAboutBlankURL)));
+  ASSERT_TRUE(NavigateToURL(shell(), GURL(url::kAboutBlankURL)));
 
   // The initial accessible returned should have state STATE_SYSTEM_BUSY while
   // the accessibility tree is being requested from the renderer.