dcef9a2922317cb2849f397366b6c56d755db6c9 logs: add timing information to FlushStateToDisk() (James O'Beirne)
41edaf227a69bc4846d5996675e8763fdfe0f367 logs: add BCLog::Timer and related macros (James O'Beirne)
Pull request description:
It's currently annoying to detect FlushStateToDisk() calls when benchmarking since they have to be inferred from a drop in coins count from the `UpdateTip: ` log messages. This adds a new logging utility, `BCLog::Timer`, and some related macros that are generally useful for printing timing-related logging messages, and a message that is unconditionally written when the coins cache is flushed to disk.
```
2019-09-04T20:17:51Z FlushStateToDisk: write block and undo data to disk completed (3ms)
2019-09-04T20:17:51Z FlushStateToDisk: write block index to disk completed (370ms)
2019-09-04T20:17:51Z FlushStateToDisk: write coins cache to disk (2068451 coins, 294967kB) completed (21481ms)
```
---
Backport of Core PR16805