Use lock-free lazy initialization for static histogram references

net/base/connection_type_histograms.cc

Index: net/base/connection_type_histograms.cc
===================================================================
--- net/base/connection_type_histograms.cc	(revision 80382)
+++ net/base/connection_type_histograms.cc	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -21,13 +21,9 @@
 // Each histogram has an unused bucket at the end to allow seamless future
 // expansion.
 void UpdateConnectionTypeHistograms(ConnectionType type) {
-  // TODO(wtc): Bug 74467 Move these stats up to a higher level, where the
-  // explicit static (shown below) and the implicit statics (inside the
-  // HISTOGRAM macros) will be thread safe.
-#if 0  // Don't do anything for now.
+  // TODO(wtc): Bug 74467 Move these stats up to a higher level.
+  static bool had_connection_type[NUM_OF_CONNECTION_TYPES];  // Default false.
 
-  static bool had_connection_type[NUM_OF_CONNECTION_TYPES];
-
   if (type >= 0 && type < NUM_OF_CONNECTION_TYPES) {
     if (!had_connection_type[type]) {
       had_connection_type[type] = true;
@@ -40,7 +36,6 @@
   } else {
     NOTREACHED();  // Someone's logging an invalid type!
   }
-#endif  // 0
 }
 
 }  // namespace net