Use lock-free lazy initialization for static histogram references

content/browser/renderer_host/buffered_resource_handler.cc

 // 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.
 
 #include "content/browser/renderer_host/buffered_resource_handler.h"
 
 #include <vector>
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
@@ skipping 11 matching lines @@
 #include "net/base/mime_util.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_response_headers.h"
 #include "webkit/plugins/npapi/plugin_list.h"
 
 namespace {
 
 void RecordSnifferMetrics(bool sniffing_blocked,
                           bool we_would_like_to_sniff,
                           const std::string& mime_type) {
-  scoped_refptr<base::Histogram> nosniff_usage =
-      base::BooleanHistogram::FactoryGet(
-          "nosniff.usage", base::Histogram::kUmaTargetedHistogramFlag);
+  static base::Histogram* nosniff_usage(NULL);
+  if (!nosniff_usage)
+    nosniff_usage = base::BooleanHistogram::FactoryGet(
+        "nosniff.usage", base::Histogram::kUmaTargetedHistogramFlag);
   nosniff_usage->AddBoolean(sniffing_blocked);
 
   if (sniffing_blocked) {
-    scoped_refptr<base::Histogram> nosniff_otherwise =
-        base::BooleanHistogram::FactoryGet(
-            "nosniff.otherwise", base::Histogram::kUmaTargetedHistogramFlag);
+    static base::Histogram* nosniff_otherwise(NULL);
+    if (!nosniff_otherwise)
+      nosniff_otherwise = base::BooleanHistogram::FactoryGet(
+          "nosniff.otherwise", base::Histogram::kUmaTargetedHistogramFlag);
     nosniff_otherwise->AddBoolean(we_would_like_to_sniff);
 
-    scoped_refptr<base::Histogram> nosniff_empty_mime_type =
-        base::BooleanHistogram::FactoryGet(
-            "nosniff.empty_mime_type",
-            base::Histogram::kUmaTargetedHistogramFlag);
+    static base::Histogram* nosniff_empty_mime_type(NULL);
+    if (!nosniff_empty_mime_type)
+      nosniff_empty_mime_type = base::BooleanHistogram::FactoryGet(
+          "nosniff.empty_mime_type",
+          base::Histogram::kUmaTargetedHistogramFlag);
     nosniff_empty_mime_type->AddBoolean(mime_type.empty());
   }
 }
 
 }  // namespace
 
 BufferedResourceHandler::BufferedResourceHandler(ResourceHandler* handler,
                                                  ResourceDispatcherHost* host,
                                                  net::URLRequest* request)
     : real_handler_(handler),
@@ skipping 425 matching lines @@
   wait_for_plugins_ = false;
   if (!request_)
     return;
 
   ResourceDispatcherHostRequestInfo* info =
       ResourceDispatcherHost::InfoForRequest(request_);
   host_->PauseRequest(info->child_id(), info->request_id(), false);
   if (!CompleteResponseStarted(info->request_id(), false))
     host_->CancelRequest(info->child_id(), info->request_id(), false);
 }