Federate platform docs against AndroidX

Bug: 76692459
Test: make docs
Change-Id: If1523ee47bcc58151a641938ac6f4a6e7ae1af0b
diff --git a/Android.mk b/Android.mk
index e219661..d7d9c90 100644
--- a/Android.mk
+++ b/Android.mk
@@ -252,6 +252,11 @@
 		-federate SupportLib https://developer.android.com \
 		-federationapi SupportLib prebuilts/sdk/current/support-api.txt
 
+# Federate AndroidX references against local API file.
+framework_docs_LOCAL_DROIDDOC_OPTIONS += \
+		-federate AndroidX https://developer.android.com \
+		-federationapi AndroidX prebuilts/sdk/current/androidx-api.txt
+
 # ====  Public API diff ===========================
 include $(CLEAR_VARS)