libbinder: automatic unlink, print cached desc

This improves the logs in cases where there is no IPC overhead from
doing so.

Bug: 145692765
Test: boot
Change-Id: I3ca9605b369afd321cabd39f57c3e75a7b17c12d
diff --git a/libs/binder/BpBinder.cpp b/libs/binder/BpBinder.cpp
index 238c9dc..f16c39c 100644
--- a/libs/binder/BpBinder.cpp
+++ b/libs/binder/BpBinder.cpp
@@ -435,7 +435,8 @@
     Vector<Obituary>* obits = mObituaries;
     if(obits != nullptr) {
         if (!obits->isEmpty()) {
-            ALOGI("onLastStrongRef automatically unlinking death recipients");
+            ALOGI("onLastStrongRef automatically unlinking death recipients: %s",
+                  mDescriptorCache.size() ? String8(mDescriptorCache).c_str() : "<uncached descriptor>");
         }
 
         if (ipc) ipc->clearDeathNotification(mHandle, this);