Optimize use of "new DexFile" in vogar.

new DexFile is very expensive, as ART will do a bunch of
verifications on it. This CL caches DexFile objects in
ClassPathScanner to avoid creating them again and again.

test: run-libcore-tests.sh
Change-Id: I75439bbfa8155124fe02ae65c297ff2615e55ee1
1 file changed