Add LOCAL_FINDBUGS_FLAGS to support custom findbugs flags.

Use LOCAL_FINDBUGS_FLAGS to specify findbugs command line flags.
To use findbugs filters:
LOCAL_FINDBUGS_FLAGS := -exclude $(LOCAL_PATH)/exclude.xml -include \
                        $(LOCAL_PATH)/include.xml

where exclude.xml and include.xml are filter files.
The build system automatically adds the filter files as dependency of
findbugs' output xml.

Bug: 24948760
Change-Id: I82502c0ade910c5255001fa5f390316137ce0be6
diff --git a/core/java.mk b/core/java.mk
index f9305df..cfae48d 100644
--- a/core/java.mk
+++ b/core/java.mk
@@ -591,13 +591,13 @@
 endif
 
 findbugs_xml := $(intermediates.COMMON)/findbugs.xml
-$(findbugs_xml) : PRIVATE_AUXCLASSPATH := $(addprefix -auxclasspath ,$(strip \
-								$(call normalize-path-list,$(filter %.jar,\
-										$(full_java_libs)))))
-$(findbugs_xml) : $(full_classes_jar)
+$(findbugs_xml): PRIVATE_AUXCLASSPATH := $(addprefix -auxclasspath ,$(strip \
+    $(call normalize-path-list,$(filter %.jar,$(full_java_libs)))))
+$(findbugs_xml): PRIVATE_FINDBUGS_FLAGS := $(LOCAL_FINDBUGS_FLAGS)
+$(findbugs_xml) : $(full_classes_jar) $(filter %.xml, $(LOCAL_FINDBUGS_FLAGS))
 	@echo Findbugs: $@
 	$(hide) $(FINDBUGS) -textui -effort:min -xml:withMessages \
-		$(PRIVATE_AUXCLASSPATH) \
+		$(PRIVATE_AUXCLASSPATH) $(PRIVATE_FINDBUGS_FLAGS) \
 		$< \
 		> $@