Treat TryFailThrowable error prone check as error

Enabling the option detected a problem in URLConnectionTest
so this fixes that.

Test: m -j -l32 javac-check-core-tests RUN_ERROR_PRONE=true
run org.apache.harmony.luni.tests.java.net.URLConnectionTest
test using vogar and CTS
Bug: 31507496
Change-Id: Ie3f150e79fc1e58f812bf5c81181a68dae752271
diff --git a/JavaLibrary.mk b/JavaLibrary.mk
index ffca748..43ea9d6 100644
--- a/JavaLibrary.mk
+++ b/JavaLibrary.mk
@@ -214,6 +214,7 @@
 	nist-pkix-tests \
 	sqlite-jdbc
 LOCAL_JAVACFLAGS := $(local_javac_flags)
+LOCAL_ERROR_PRONE_FLAGS := -Xep:TryFailThrowable:ERROR
 LOCAL_JAVA_LANGUAGE_VERSION := 1.8
 LOCAL_MODULE := core-tests
 LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/JavaLibrary.mk