xml: Fix behavior of time graph view for experiment analyses

xml: Fix behavior of time graph view for experiment analyses

Reverts part of commit f3dac92a8f96850f47c1be3279cdab71b8857b65 which was
reverting another commit

When an XML analysis is for an experiment, the time graph view remains empty
because the view is never built with the experiment, only with its children

Change-Id: Ib3d12fc6765cdd66a5846950b032240e1add7496
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/77984
Reviewed-by: Hudson CI
Tested-by: Jean-Christian Kouame <jean-christian.kouame@ericsson.com>