Allow for opt-in of proguard shrinking of tests with new flag

By adding 'shrinktests' to LOCAL_PROGUARD_ENABLED, the -dontshrink
flag will be omitted from the resulting proguard config allowing
tests to have unnecessary classes removed before dexxing.

Clockwork is running into 64k method limits on some tests which
depend on GmsCore. On 4.4W (klp-modular-dev) we don't have the
option for multi-dex so proguard is the only solution here.

This change leaves the default behavior unchanged. Shrinking is
still disabled for tests by default unless the 'shrinktests'
flag is set in the Makefile.

Change-Id: Ib586ae9e7f617072b41e95742559bf7c8a6a6ce1
diff --git a/core/java.mk b/core/java.mk
index 8863ac2..79be181 100644
--- a/core/java.mk
+++ b/core/java.mk
@@ -378,7 +378,7 @@
 
 # Run proguard if necessary, otherwise just copy the file.
 ifdef LOCAL_PROGUARD_ENABLED
-ifneq ($(filter-out full custom nosystem obfuscation optimization,$(LOCAL_PROGUARD_ENABLED)),)
+ifneq ($(filter-out full custom nosystem obfuscation optimization shrinktests,$(LOCAL_PROGUARD_ENABLED)),)
     $(warning while processing: $(LOCAL_MODULE))
     $(error invalid value for LOCAL_PROGUARD_ENABLED: $(LOCAL_PROGUARD_ENABLED))
 endif
@@ -395,6 +395,9 @@
 # If this is a test package, add proguard keep flags for tests.
 ifneq ($(LOCAL_INSTRUMENTATION_FOR)$(filter tests,$(LOCAL_MODULE_TAGS)),)
 proguard_flags += -include $(BUILD_SYSTEM)/proguard_tests.flags
+ifeq ($(filter shrinktests,$(LOCAL_PROGUARD_ENABLED)),)
+proguard_flags += -dontshrink # don't shrink tests by default
+endif # shrinktests
 endif # test package
 ifeq ($(filter obfuscation,$(LOCAL_PROGUARD_ENABLED)),)
 # By default no obfuscation