honeycomb: instrumenting save_child_position()
honeycomb: instrumenting save_child_position()

From this trace:
https://ui.honeycomb.io/appsembler/datasets/tahoe-hawthorn-prod/result/AKJBe6fg7ra/trace/eah2UsbDDe3

it appears that a call to `save_child_position()` took about 30s and
we don't have any instrumentation inside there.

So this is the next step to figure out where the time is disappearing
to in that function.

appsembler/edx-platform,appsembler/edx-platform,appsembler/edx-platform,appsembler/edx-platform