Use lock-free lazy initialization for static histogram references

net/disk_cache/stats.cc

Index: net/disk_cache/stats.cc
===================================================================
--- net/disk_cache/stats.cc	(revision 79771)
+++ net/disk_cache/stats.cc	(working copy)
@@ -116,7 +116,7 @@
   return StoreStats(backend, *address, stats);
 }
 
-Stats::Stats() : backend_(NULL) {
+Stats::Stats() : backend_(NULL), size_histogram_(NULL) {
 }
 
 Stats::~Stats() {
@@ -146,7 +146,7 @@
   if (first_time) {
     first_time = false;
     // ShouldReportAgain() will re-enter this object.
-    if (!size_histogram_.get() && backend->cache_type() == net::DISK_CACHE &&
+    if (!size_histogram_ && backend->cache_type() == net::DISK_CACHE &&
         backend->ShouldReportAgain()) {
       // Stats may be reused when the cache is re-created, but we want only one
       // histogram at any given time.