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/base/logging.cc b/runtime/base/logging.cc
index 0764b87..0ae7863 100644
--- a/runtime/base/logging.cc
+++ b/runtime/base/logging.cc
@@ -91,7 +91,7 @@
     gProgramInvocationShortName.reset(new std::string((last_slash != nullptr) ? last_slash + 1
                                                                            : argv[0]));
   } else {
-    // TODO: fall back to /proc/self/cmdline when argv is NULL on Linux.
+    // TODO: fall back to /proc/self/cmdline when argv is null on Linux.
     gCmdLine.reset(new std::string("<unset>"));
   }
   const char* tags = getenv("ANDROID_LOG_TAGS");