Add a debug assert to track down infinite loop

Bug: 26980851
Change-Id: I326983ab367782048311b6cf06d800f72837e38e
diff --git a/libs/hwui/Android.mk b/libs/hwui/Android.mk
index 1fb9ac5..939b9f6 100644
--- a/libs/hwui/Android.mk
+++ b/libs/hwui/Android.mk
@@ -250,7 +250,8 @@
     tests/unit/SkiaBehaviorTests.cpp \
     tests/unit/StringUtilsTests.cpp \
     tests/unit/TextDropShadowCacheTests.cpp \
-    tests/unit/VectorDrawableTests.cpp
+    tests/unit/VectorDrawableTests.cpp \
+    tests/unit/GradientCacheTests.cpp
 
 ifeq (true, $(HWUI_NEW_OPS))
     LOCAL_SRC_FILES += \