Disable R8 for DocumentsUI

This failure seems related to R8:

https://sponge.corp.google.com/target?show=FAILED&sortBy=STATUS&id=4f1b303e-ef57-4dc6-9ebb-95ca5cda398e&target=com.android.documentsui.tests

Test: Run DucumentsUI tests, and the failure above is gone.
Change-Id: Ib04f5400fa78823cfc8b5294d247f08ffd184176
Merged-In: I828190c8742375abb1d20376010f203e45e0f0cf
diff --git a/Android.mk b/Android.mk
index 349d78e..97eb47d 100644
--- a/Android.mk
+++ b/Android.mk
@@ -4,6 +4,9 @@
 LOCAL_MODULE_TAGS := optional
 LOCAL_PRIVILEGED_MODULE := true
 
+# See b/74746744.
+LOCAL_USE_R8=false
+
 LOCAL_SRC_FILES := $(call all-java-files-under, src)
 
 LOCAL_STATIC_JAVA_LIBRARIES += guava