Reset accessibility if it gets out of sync.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index e2bf47bc3e6b179002fb72ed4f1a3fdf6525290b..1f228805e7651e4c4876b0ca92393e503dc9ec18 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -70,6 +70,9 @@ namespace content {
 
 namespace {
 
+// The next value to use for the accessibility reset token.
+int g_next_accessibility_reset_token = 1;
+
 // The (process id, routing id) pair that identifies one RenderFrame.
 typedef std::pair<int32, int32> RenderFrameHostID;
 typedef base::hash_map<RenderFrameHostID, RenderFrameHostImpl*>
@@ -189,6 +192,9 @@ RenderFrameHostImpl::RenderFrameHostImpl(RenderViewHostImpl* render_view_host,
       navigations_suspended_(false),
       is_waiting_for_beforeunload_ack_(false),
       unload_ack_is_for_cross_site_transition_(false),
+      accessibility_reset_token_(0),
+      accessibility_reset_count_(0),
+      no_create_browser_accessibility_manager_for_testing_(false),
       weak_ptr_factory_(this) {
   frame_tree_->RegisterRenderFrameHost(this);
   GetProcess()->AddRoute(routing_id_, this);
@@ -479,8 +485,18 @@ void RenderFrameHostImpl::AccessibilityHitTest(const gfx::Point& point) {
 }
 
 void RenderFrameHostImpl::AccessibilityFatalError() {
-  Send(new AccessibilityMsg_FatalError(routing_id_));
   browser_accessibility_manager_.reset(NULL);
+  if (accessibility_reset_token_)
+    return;
+
+  accessibility_reset_count_++;
+  if (accessibility_reset_count_ >= kMaxAccessibilityResets) {
+    Send(new AccessibilityMsg_FatalError(routing_id_));
+  } else {
+    accessibility_reset_token_ = g_next_accessibility_reset_token++;
+    UMA_HISTOGRAM_COUNTS("Accessibility.FrameResetCount", 1);
+    Send(new AccessibilityMsg_Reset(routing_id_, accessibility_reset_token_));
+  }
 }
 
 gfx::AcceleratedWidget
@@ -756,6 +772,7 @@ void RenderFrameHostImpl::OnDidCommitProvisionalLoad(const IPC::Message& msg) {
     return;
   }
 
+  accessibility_reset_count_ = 0;
   frame_tree_node()->navigator()->DidNavigate(this, validated_params);
 }
 
@@ -1081,7 +1098,17 @@ void RenderFrameHostImpl::OnBeginNavigation(
 }
 
 void RenderFrameHostImpl::OnAccessibilityEvents(
-    const std::vector<AccessibilityHostMsg_EventParams>& params) {
+    const std::vector<AccessibilityHostMsg_EventParams>& params,
+    int reset_token) {
+  // Don't process this IPC if either we're waiting on a reset and this
+  // IPC doesn't have the matching token ID, or if we're not waiting on a
+  // reset but this message includes a reset token.
+  if (accessibility_reset_token_ != reset_token) {
+    Send(new AccessibilityMsg_Events_ACK(routing_id_));
+    return;
+  }
+  accessibility_reset_token_ = 0;
+
   RenderWidgetHostViewBase* view = static_cast<RenderWidgetHostViewBase*>(
       render_view_host_->GetView());
 
@@ -1156,17 +1183,18 @@ void RenderFrameHostImpl::OnAccessibilityEvents(
 
 void RenderFrameHostImpl::OnAccessibilityLocationChanges(
     const std::vector<AccessibilityHostMsg_LocationChangeParams>& params) {
+  if (accessibility_reset_token_)
+    return;
+
   RenderWidgetHostViewBase* view = static_cast<RenderWidgetHostViewBase*>(
       render_view_host_->GetView());
   if (view && RenderFrameHostImpl::IsRFHStateActive(rfh_state())) {
     AccessibilityMode accessibility_mode = delegate_->GetAccessibilityMode();
     if (accessibility_mode & AccessibilityModeFlagPlatform) {
-      if (!browser_accessibility_manager_) {
-        browser_accessibility_manager_.reset(
-            view->CreateBrowserAccessibilityManager(this));
-      }
-      if (browser_accessibility_manager_)
-        browser_accessibility_manager_->OnLocationChanges(params);
+      BrowserAccessibilityManager* manager =
+          GetOrCreateBrowserAccessibilityManager();
+      if (manager)
+        manager->OnLocationChanges(params);
     }
     // TODO(aboxhall): send location change events to web contents observers too
   }
@@ -1474,9 +1502,14 @@ BrowserAccessibilityManager*
   RenderWidgetHostViewBase* view = static_cast<RenderWidgetHostViewBase*>(
       render_view_host_->GetView());
   if (view &&
-      !browser_accessibility_manager_) {
+      !browser_accessibility_manager_ &&
+      !no_create_browser_accessibility_manager_for_testing_) {
     browser_accessibility_manager_.reset(
         view->CreateBrowserAccessibilityManager(this));
+    if (browser_accessibility_manager_)
+      UMA_HISTOGRAM_COUNTS("Accessibility.FrameEnabledCount", 1);
+    else
+      UMA_HISTOGRAM_COUNTS("Accessibility.FrameDidNotEnableCount", 1);
   }
   return browser_accessibility_manager_.get();
 }