Mark inspector-protocol/heap-profiler/heap-snapshot-with-detached-dom-tree.html as flaky

TBR=alph@chromium.org
BUG=313217

Review URL: https://codereview.chromium.org/54363002

git-svn-id: svn://svn.chromium.org/blink/trunk@161039 bbb929c8-8fbe-4397-9dbb-9b2b20218538