WebView: fix TracingController example usage

This fixes a minor mistake in the TracingController class usage. The
example previously used a bare `CATEGORIES_WEB_DEVELOPER` instead of
`TracingConfig.CATEGORIES_WEB_DEVELOPER`.

Bug: 116227333
Test: make docs
Change-Id: I648dd0d5e61666e61adb27303c185013bd80b0ea
1 file changed