Fix recents entry delay

- Start loading things after we drew our first frame.
- Don't load high res task until low res tasks have been loaded:
In case the snapshot is already in cache in system_server the
low-res task loader will load the full res snapshot, leading to
GC pressure due to registerNativeAlloc. Now, if both task loader
load the same snapshot at the same time we are very likely
to trigger a blocking GC alloc.

Test: Open recents, look at systrace
Change-Id: I10c263dc8929742611ad9fbb32f65bc8ac3100bd
Fixes: 36851903
Bug: 32668632