Observed on Linux ToT build at revision #488643.

Steps to reproduce:
1. Launch chrome with --enable-ui-devtools=9332.
2. Navigate to chrome://inspect#other.
3. Click on the link to open the UI DevTools front end.
4. In the hierarchical listing of the window/widget/view elements, right click on the RootWindow element and select "Expand all".

What happens:
The hierarchical listing of window/widget/view elements belonging to the browser instance will initially be shown. But when attempting to inspect some of these elements, the majority of the node tree will disappear, though the browser UI itself will remain unchanged.

What should happen instead:
The hierarchical listing of nodes in UI DevTools should always remain in sync with the actual browser UI.

Note: this does not seem to reproduce with a remote connection (i.e., when a ToT build is being inspected, but DevTools is open in a separate browser instance such as Chrome stable for Linux).