Replace NULL with nullptr

Also fixed some lines that were too long, and a few other minor
details.

Change-Id: I6efba5fb6e03eb5d0a300fddb2a75bf8e2f175cb
diff --git a/runtime/indirect_reference_table_test.cc b/runtime/indirect_reference_table_test.cc
index fe1b8f0..c20002b 100644
--- a/runtime/indirect_reference_table_test.cc
+++ b/runtime/indirect_reference_table_test.cc
@@ -216,7 +216,7 @@
   ASSERT_EQ(0U, irt.Capacity()) << "temporal del not empty";
   CheckDump(&irt, 0, 0);
 
-  // nullptr isn't a valid iref.
+  // null isn't a valid iref.
   ASSERT_TRUE(irt.Get(nullptr) == nullptr);
 
   // Stale lookup.