Perfetto UI - dc64278a342f53

ui: separate modal dialog state by trace

Where applicable, tie the modal dialog state to a trace. Where an
explicit trace context is available, inject it into the dialog state.
Otherwise, infer it from the currently active trace if there is one,
otherwise the app instance.

For android-graphics/sokatoa#4112

Signed-off-by: Christian W. Damus <cdamus.ext@eclipsesource.com>