content: convert accessibility notifications to observer usage

content/public/browser/render_view_host.h

Index: content/public/browser/render_view_host.h
diff --git a/content/public/browser/render_view_host.h b/content/public/browser/render_view_host.h
index 10f7724667ab8316ea671ee425ccbd0045af6f1d..1d759eb19bda80af6ab5795a709549ab528293fb 100644
--- a/content/public/browser/render_view_host.h
+++ b/content/public/browser/render_view_host.h
@@ -278,6 +278,14 @@ class CONTENT_EXPORT RenderViewHost : virtual public RenderWidgetHost {
   // Informs the renderer process of a change in timezone.
   virtual void NotifyTimezoneChange() = 0;
 
+  // Set accessibility callbacks.
+  virtual void SetAccessibilityLayoutCompleteCallbackForTesting(
+      const base::Closure& callback) = 0;
+  virtual void SetAccessibilityLoadCompleteCallbackForTesting(
+      const base::Closure& callback) = 0;
+  virtual void SetAccessibilityOtherCallbackForTesting(
+      const base::Closure& callback) = 0;
+
 #if defined(OS_ANDROID)
   // Selects and zooms to the find result nearest to the point (x,y)
   // defined in find-in-page coordinates.