Fixes a performance bottleneck in `ConversationFragment` caused by expensive calculations in `ConversationItemDecorations.hasHeader()`. This method is invoked in `RecyclerView.ItemDecoration.getItemOffsets()`, which runs on every layout pass and happens frequently during scrolling.
The most expensive calculation in `hasHeader()` is `toEpochDay()`. That method calls `Long.toLocalDate()`, which clones a `TimeZone` object on each call. Upon opening one conversation (without scrolling), I observed that `toEpochDay()` was called over 1000 times in less than a second, rapidly allocating memory and causing garbage collection pressure that potentially leads to ANRs.
We only need to calculate `hasHeader()` once for each conversation element, so caching the result of that method will eliminate the unnecessary calculations and improve the memory usage of `ConversationFragment`.
8a057168ae