Use IAccessible2 to detect screen reader in Win Aura.

See bug for context. This change makes calling
an IAccessible2 API on the web content's root
accessible object enable full web accessibility
support. This supports popular Windows screen readers
but won't enable accessibility under other
circumstances when we don't need it.

However, this doesn't always detect the screen
reader right away when the app opens, so we also
modify Views accessibility to detect IAccessible2
and query the IAccessible2 API on each web view.
That catches use of IAccessible2 immediately.

BUG=292719

Review URL: https://chromiumcodereview.appspot.com/23531055

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@223416 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/accessibility/browser_accessibility_win.cc

@@ -15,6 +15,7 @@
 #include "base/win/scoped_comptr.h"
 #include "base/win/windows_version.h"
 #include "content/browser/accessibility/browser_accessibility_manager_win.h"
+#include "content/browser/accessibility/browser_accessibility_state_impl.h"
 #include "content/common/accessibility_messages.h"
 #include "content/public/common/content_client.h"
 #include "ui/base/accessibility/accessible_text_utils.h"
@@ -2651,6 +2652,12 @@ STDMETHODIMP BrowserAccessibilityWin::QueryService(REFGUID guidService,
   if (!instance_active_)
     return E_FAIL;
 
+  // The system uses IAccessible APIs for many purposes, but only
+  // assistive technology like screen readers uses IAccessible2.
+  // Enable full accessibility support when IAccessible2 APIs are queried.
+  if (riid == IID_IAccessible2)
+    BrowserAccessibilityStateImpl::GetInstance()->EnableAccessibility();
+
   if (guidService == GUID_IAccessibleContentDocument) {
     // Special Mozilla extension: return the accessible for the root document.
     // Screen readers use this to distinguish between a document loaded event

ui/views/accessibility/native_view_accessibility_win.cc

@@ -12,6 +12,7 @@
 
 #include "base/memory/singleton.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/win/scoped_comptr.h"
 #include "base/win/windows_version.h"
 #include "third_party/iaccessible2/ia2_api_all.h"
 #include "ui/base/accessibility/accessible_text_utils.h"
@@ -44,6 +45,15 @@ class AccessibleWebViewRegistry {
   // |top_view|'s view hierarchy, if any.
   IAccessible* GetAccessibleFromWebView(View* top_view, long child_id);
 
+  // The system uses IAccessible APIs for many purposes, but only
+  // assistive technology like screen readers uses IAccessible2.
+  // Call this method to note that the IAccessible2 interface was queried and
+  // that WebViews should be proactively notified that this interface will be
+  // used. If this is enabled for the first time, this will explicitly call
+  // QueryService with an argument of IAccessible2 on all WebViews, otherwise
+  // it will just do it from now on.
+  void EnableIAccessible2Support();
+
  private:
   friend struct DefaultSingletonTraits<AccessibleWebViewRegistry>;
   AccessibleWebViewRegistry();
@@ -51,6 +61,8 @@ class AccessibleWebViewRegistry {
 
   IAccessible* AccessibleObjectFromChildId(View* web_view, long child_id);
 
+  void QueryIAccessible2Interface(View* web_view);
+
   // Set of all web views. We check whether each one is contained in a
   // top view dynamically rather than keeping track of a map.
   std::set<View*> web_views_;
@@ -62,12 +74,18 @@ class AccessibleWebViewRegistry {
   // corresponding to |last_top_view_|.
   View* last_web_view_;
 
+  // If IAccessible2 support is enabled, we query the IAccessible2 interface
+  // of WebViews proactively when they're registered, so that they are
+  // aware that they need to support this interface.
+  bool iaccessible2_support_enabled_;
+
   DISALLOW_COPY_AND_ASSIGN(AccessibleWebViewRegistry);
 };
 
 AccessibleWebViewRegistry::AccessibleWebViewRegistry()
     : last_top_view_(NULL),
-      last_web_view_(NULL) {
+      last_web_view_(NULL),
+      iaccessible2_support_enabled_(false) {
 }
 
 AccessibleWebViewRegistry* AccessibleWebViewRegistry::GetInstance() {
@@ -77,6 +95,9 @@ AccessibleWebViewRegistry* AccessibleWebViewRegistry::GetInstance() {
 void AccessibleWebViewRegistry::RegisterWebView(View* web_view) {
   DCHECK(web_views_.find(web_view) == web_views_.end());
   web_views_.insert(web_view);
+
+  if (iaccessible2_support_enabled_)
+    QueryIAccessible2Interface(web_view);
 }
 
 void AccessibleWebViewRegistry::UnregisterWebView(View* web_view) {
@@ -120,6 +141,16 @@ IAccessible* AccessibleWebViewRegistry::GetAccessibleFromWebView(
   return NULL;
 }
 
+void AccessibleWebViewRegistry::EnableIAccessible2Support() {
+  if (iaccessible2_support_enabled_)
+    return;
+  iaccessible2_support_enabled_ = true;
+  for (std::set<View*>::iterator iter = web_views_.begin();
+       iter != web_views_.end(); ++iter) {
+    QueryIAccessible2Interface(*iter);
+  }
+}
+
 IAccessible* AccessibleWebViewRegistry::AccessibleObjectFromChildId(
     View* web_view,
     long child_id) {
@@ -139,6 +170,20 @@ IAccessible* AccessibleWebViewRegistry::AccessibleObjectFromChildId(
   return NULL;
 }
 
+void AccessibleWebViewRegistry::QueryIAccessible2Interface(View* web_view) {
+  IAccessible* web_view_accessible = web_view->GetNativeViewAccessible();
+  if (!web_view_accessible)
+    return;
+
+  base::win::ScopedComPtr<IServiceProvider> service_provider;
+  if (S_OK != web_view_accessible->QueryInterface(service_provider.Receive()))
+    return;
+  base::win::ScopedComPtr<IAccessible2> iaccessible2;
+  service_provider->QueryService(
+      IID_IAccessible, IID_IAccessible2,
+      reinterpret_cast<void**>(iaccessible2.Receive()));
+}
+
 }  // anonymous namespace
 
 // static
@@ -1026,6 +1071,9 @@ STDMETHODIMP NativeViewAccessibilityWin::QueryService(
   if (!view_)
     return E_FAIL;
 
+  if (riid == IID_IAccessible2)
+    AccessibleWebViewRegistry::GetInstance()->EnableIAccessible2Support();
+
   if (guidService == IID_IAccessible ||
       guidService == IID_IAccessible2 ||
       guidService == IID_IAccessibleText)  {