Standalone system server jars are dynamically loaded by system server
using a `PathClassLoader` whose parent is `SYSTEMSERVERCLASSPATH`. They
are listed in `PRODUCT_STANDALONE_SYSTEM_SERVER_JARS` and
`PRODUCT_APEX_STANDALONE_SYSTEM_SERVER_JARS` in Makefile. We need to
dexpreopt them to achieve better performance.
Bug: 203198541
Test: m nothing
Test: -
1. Add a standalone system server jar (e.g., by patching
aosp/1906158)
2. Build a system image.
3. See the odex and vdex files generated in
$ANDROID_PRODUCT_OUT/system/framework/oat/
4. Flash the image to a device.
5. Run `atest art_standalone_dexpreopt_tests`.
Change-Id: I358a62d34989c5c8eba12e18fe6167e0b72ff69d
389a647320