Add new droiddoc option for project-specific secondary html input/output paths.

Change-Id: Id9c3dc4e7cfcc26c04e4d1aeb6617e3e6b92114b
diff --git a/core/droiddoc.mk b/core/droiddoc.mk
index 9f42933..03a5011 100644
--- a/core/droiddoc.mk
+++ b/core/droiddoc.mk
@@ -147,6 +147,11 @@
 else
 $(full_target): PRIVATE_DROIDDOC_HTML_DIR := 
 endif
+ifneq ($(strip $(LOCAL_ADDITIONAL_HTML_DIR)),)
+$(full_target): PRIVATE_ADDITIONAL_HTML_DIR := -htmldir2 $(LOCAL_PATH)/$(LOCAL_ADDITIONAL_HTML_DIR)
+else
+$(full_target): PRIVATE_ADDITIONAL_HTML_DIR :=
+endif
 
 # TODO: not clear if this is used any more
 $(full_target): PRIVATE_LOCAL_PATH := $(LOCAL_PATH)
@@ -168,6 +173,7 @@
                 -docletpath $(PRIVATE_DOCLETPATH) \
                 -templatedir $(PRIVATE_CUSTOM_TEMPLATE_DIR) \
                 $(PRIVATE_DROIDDOC_HTML_DIR) \
+                $(PRIVATE_ADDITIONAL_HTML_DIR) \
                 $(addprefix -bootclasspath ,$(PRIVATE_BOOTCLASSPATH)) \
                 $(addprefix -classpath ,$(PRIVATE_CLASSPATH)) \
                 -sourcepath $(PRIVATE_SOURCE_PATH)$(addprefix :,$(PRIVATE_CLASSPATH)) \