Enable PDF accessibility when RenderFrame's accessibility mode changes.

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 4167222969def20c760b86eb6e739add6fd9986a..2a7ae70004b816244f8c2f898330a7aa0f07df94 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -2111,11 +2111,12 @@ void RenderFrameImpl::OnSetAccessibilityMode(AccessibilityMode new_mode) {
     delete render_accessibility_;
     render_accessibility_ = NULL;
   }
-  if (accessibility_mode_ == AccessibilityModeOff)
-    return;
 
   if (accessibility_mode_ & AccessibilityModeFlagFullTree)
     render_accessibility_ = new RenderAccessibilityImpl(this);
+
+  FOR_EACH_OBSERVER(RenderFrameObserver, observers_,
+                    AccessibilityModeChanged());
 }
 
 void RenderFrameImpl::OnSnapshotAccessibilityTree(int callback_id) {