am e35d9280: cherrypick from jb-dev Change-Id: Idecee238d8872ca1c32a80d13ad61bacf89c39f7 docs: Systrace tool documentation

* commit 'e35d9280d6cd5bfca13f9f1c3e8e90636e00c6cf':
  cherrypick from jb-dev Change-Id: Idecee238d8872ca1c32a80d13ad61bacf89c39f7 docs: Systrace tool documentation