break up event-log-tags; generate java source files with constants

Construct the /system/etc/event-log-tags file by unioning together any
*.logtags files included in LOCAL_SRC_FILES throughout the system (with
appropriate error checking for dup tag numbers, etc.)

For java packages, generate a java source file from the logtags file for
that package that contains static integer constants for each tag name.
diff --git a/core/Makefile b/core/Makefile
index 2f316ca..05a9b86 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -472,6 +472,27 @@
 
 
 # -----------------------------------------------------------------
+
+.PHONY: event-log-tags
+
+event_log_tags_file := $(TARGET_OUT)/etc/event-log-tags
+ALL_PREBUILT += $(event_log_tag_file)
+
+# Include tags from all packages included in this product.
+event_log_tags_src := \
+    $(sort $(foreach m,\
+      $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES) \
+      $(call module-names-for-tag-list,user), \
+      $(ALL_MODULES.$(m).EVENT_LOG_TAGS)))
+
+$(event_log_tags_file): PRIVATE_SRC_FILES := $(event_log_tags_src)
+$(event_log_tags_file): $(event_log_tags_src)
+	$(hide) mkdir -p $(dir $@)
+	$(hide) build/tools/merge-event-log-tags.py -o $@ $(PRIVATE_SRC_FILES)
+
+event-log-tags: $(event_log_tags_file)
+
+# -----------------------------------------------------------------
 # Build a keystore with the authorized keys in it, used to verify the
 # authenticity of downloaded OTA packages.
 #