This allow Metalava to generate public-dex file when user specify
dex_api_filename.
This blocks how we try java9 for droiddoc since "hiddenapi-lists-docs"
targets depends on libcore sources.
Test: m -j hiddenapi-lists-docs
Bug: b/78245848
Change-Id: Ic847c1123b14afb599dbf2a588885fd36e56b2cc
Merged-In: Ic847c1123b14afb599dbf2a588885fd36e56b2cc