Add browser test for WebUI URL logging

chrome/browser/ui/webui/log_web_ui_url.cc

 // Copyright 2015 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 "chrome/browser/ui/webui/log_web_ui_url.h"
 
 #include "base/hash.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/sparse_histogram.h"
 #include "chrome/common/url_constants.h"
 #include "content/public/common/url_constants.h"
 #include "url/gurl.h"
 
 #if defined(ENABLE_EXTENSIONS)
 #include "chrome/common/extensions/extension_constants.h"
 #include "extensions/common/constants.h"
 #endif
 
 namespace webui {
 
+const char kWebUICreatedForUrl[] = "WebUI.CreatedForUrl";
+
 bool LogWebUIUrl(const GURL& web_ui_url) {
   bool should_log = web_ui_url.SchemeIs(content::kChromeUIScheme) ||
                     web_ui_url.SchemeIs(content::kChromeDevToolsScheme);
 
 #if defined(ENABLE_EXTENSIONS)
   if (web_ui_url.SchemeIs(extensions::kExtensionScheme))
     should_log = web_ui_url.host() == extension_misc::kBookmarkManagerId;
 #endif
 
   if (should_log) {
     uint32 hash = base::Hash(web_ui_url.GetOrigin().spec());
-    UMA_HISTOGRAM_SPARSE_SLOWLY("WebUI.CreatedForUrl",
+    UMA_HISTOGRAM_SPARSE_SLOWLY(kWebUICreatedForUrl,
                                 static_cast<base::HistogramBase::Sample>(hash));
   }
 
   return should_log;
 }
 
 }  // namespace webui