Dump backtrace on `DeleteLocalRef` failures (to debug mmap failures).

Bug: b/228295454
Test: art/tools/buildbot-build.sh
Change-Id: I01cffe7dc284a6af270f6bc3d29f48c4a0546359
diff --git a/runtime/jni/jni_internal.cc b/runtime/jni/jni_internal.cc
index 8463bc2..7a25b4b 100644
--- a/runtime/jni/jni_internal.cc
+++ b/runtime/jni/jni_internal.cc
@@ -899,6 +899,8 @@
       // going quite the way they expect.
       LOG(WARNING) << "JNI WARNING: DeleteLocalRef(" << obj << ") "
                    << "failed to find entry";
+      // Investigating b/228295454: Scudo ERROR: internal map failure (NO MEMORY).
+      soa.Self()->DumpJavaStack(LOG_STREAM(WARNING));
     }
   }