Revert "Revert "Add docs for idle page tracking.""
Revert "Revert "Add docs for idle page tracking.""

This reverts commit b7e3edc24c1e1de0b1b937a09f5b9dfa693406b4.

Reason for revert: Reland fixed version.

Change-Id: I7a03721eda7c5a9e33dafa02f4ad41ecd5e48f5f
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto