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This defines basic build targets for a Trichrome build using the
upstream package names/configuration. The shared library APK contains
the 32-bit version of libmonochrome.so and a few autogenerated Java
pieces only at this stage, which means the total size of the three APKs
is significantly larger than Monochrome at present.

Reland fixes a conflict with another CL that went through the CL in
parallel, and fixes an issue where gn generation failed when
is_official_build=true.

Bug: 887078
Change-Id: I86082eeffef53c018ccdc13a3122ff72fed5f5e6
Reviewed-on: https://chromium-review.googlesource.com/1246728Reviewed-by: Tobias Sargeant <tobiasjs@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Commit-Queue: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595123}