Convert reportTrackThreadHeight from const varible to function
Convert reportTrackThreadHeight from const varible to function

It was giving us error while there were some cyclic dependencies.
They are fixed now but still all the other functions in this file is
using "export function" and it's good to keep the consistency here.

devtools-html/perf.html,mstange/cleopatra,devtools-html/perf.html,mstange/cleopatra