Hook up guest browser plugins to the accessibility tree.

content/browser/frame_host/render_frame_host_delegate.h

Index: content/browser/frame_host/render_frame_host_delegate.h
diff --git a/content/browser/frame_host/render_frame_host_delegate.h b/content/browser/frame_host/render_frame_host_delegate.h
index 40af1dba20c272427e2dc4af89622628cd87094e..b0ebe38f47ac7dfecf1581b3613d523baef7093e 100644
--- a/content/browser/frame_host/render_frame_host_delegate.h
+++ b/content/browser/frame_host/render_frame_host_delegate.h
@@ -137,6 +137,10 @@ class CONTENT_EXPORT RenderFrameHostDelegate {
   virtual void AccessibilityEventReceived(
       const std::vector<AXEventNotificationDetails>& details) {}
 
+  // Find a guest RenderFrameHost by its browser plugin instance id.
+  virtual RenderFrameHost* GetGuestByInstanceID(
+      int browser_plugin_instance_id);
+
 #if defined(OS_WIN)
   // Returns the frame's parent's NativeViewAccessible.
   virtual gfx::NativeViewAccessible GetParentNativeViewAccessible();