Add comment explaning assumption around symbol loading

Author: dmpots

lldb/test/Shell/Commands/command-statistics-dump.test

@@ -1,3 +1,12 @@
+# This test validates that statistics generation does not force loading
+# symbol tables. In order to avoid other sources of symbol loading we
+# create the target without loading dependents and do not actually
+# run it. Running the target is a problem because there are various
+# instrumentation plugins (e.g. ASAN) that are always enabled and force
+# symbol loading. If you see this test start to fail we may have added
+# a new source of symbol loading unexpectedly.
+
+# Build a simple test executable.
 # RUN: %clang_host -g %S/Inputs/main.c -o %t-main.exe
 
 # When we enable symbol preload and dump stats there should be a non-zero