Computer Configuration > Administrative Templates > Google Chrome - Default Settings (users can override)
Both
HKLM\Software\Policies\Google\Chrome\Recommended
Setting the policy to Enabled imports bookmarks from the previous default browser on first run. Setting the policy to Disabled or leaving it unset means no bookmarks are imported on first run. Users can trigger an import dialog and the bookmarks checkbox will be checked or unchecked to match this policy's value.