In the tick processor, in cases where there are a lot of ticks (e.g.
long running programs), JSON.stringify could throw a range exception
because the created string is too large.

Instead of creating the entire JSON string in memory, we now write the
top-level parts of the JSON manually, writing out the ticks individually
instead of all together.

Review-Url: https://codereview.chromium.org/2754683002
Cr-Commit-Position: refs/heads/master@{#43973}