Observed on both of:
* Chrome OS ToT Linux developer build (target_os = "chromeos") at revision #488643
* Chrome OS canary 62.0.3166.0

Steps to reproduce:
1. If using canary, ensure enable-ui-devtools is enabled from chrome://flags. If running from the command line, pass the flag --enable-ui-devtools=9332.
2. Navigate to chrome://inspect#other.
3. Click on the link to open the UI DevTools front end in a separate tab.
4. In the hierarchical view of window/widget/view UI elements, right-click on the RootWindow element and select "expand all".
5. Hover over the nodes in this hierarchy of UI elements.

What happens:
Nothing.

What should happen:
The corresponding UI element should be shown as highlighted in the actual native UI being inspected.

Note: Element highlighting works as expected when inspecting remotely.