Resurrect and fix inspector-protocol/heap-profiler/heap-snapshot-with-detached-dom-tree.html

I added explicit call to InspectorTest.completeTest to avoid test timeouts.

BUG=239549

Review URL: https://codereview.chromium.org/48313002

git-svn-id: svn://svn.chromium.org/blink/trunk@160710 bbb929c8-8fbe-4397-9dbb-9b2b20218538