User Gesture plumbed from Renderer to Browser's FullscreenController::RequestToLockMouse.

content/public/browser/render_view_host_delegate.h

Index: content/public/browser/render_view_host_delegate.h
diff --git a/content/public/browser/render_view_host_delegate.h b/content/public/browser/render_view_host_delegate.h
index d67099799da4118bb3c53357643722622e43d5c0..ed15cdd9d0d866768593f7ce9f5046022a6e7983 100644
--- a/content/public/browser/render_view_host_delegate.h
+++ b/content/public/browser/render_view_host_delegate.h
@@ -399,7 +399,7 @@ class CONTENT_EXPORT RenderViewHostDelegate : public IPC::Channel::Listener {
   // Requests to lock the mouse. Once the request is approved or rejected,
   // GotResponseToLockMouseRequest() will be called on the requesting render
   // view host.
-  virtual void RequestToLockMouse() {}
+  virtual void RequestToLockMouse(bool user_gesture) {}
 
   // Notification that the view has lost the mouse lock.
   virtual void LostMouseLock() {}