Record InstantExtended pref setting on startup with an UMA histogram.

chrome/browser/instant/search.cc

 // Copyright 2012 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/instant/search.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
@@ skipping 320 matching lines @@
 }
 
 bool IsInstantPrefEnabled(Profile* profile) {
   if (!profile || profile->IsOffTheRecord())
     return false;
 
   const PrefService* prefs = profile->GetPrefs();
   if (!prefs)
     return false;
 
-  return prefs->GetBoolean(GetInstantPrefName());
+  const char* pref_name = GetInstantPrefName();
+  const bool pref_value = prefs->GetBoolean(pref_name);
+
+  if (pref_name == prefs::kInstantExtendedEnabled) {
+    static bool recorded = false;

[sreeram, 2013/03/14 18:22:44]

Nit: Please add a comment about 'recorded' not being profile-specific, so this
histogram only gets recorded for the first profile that happens to call this
code.

[Alexei Svitkine (slow), 2013/03/14 18:33:12]

Done.

+    if (!recorded) {
+      UMA_HISTOGRAM_BOOLEAN("InstantExtended.PrefValue", pref_value);
+      recorded = true;
+    }
+  }
+
+  return pref_value;
 }
 
 void SetInstantExtendedPrefDefault(Profile* profile) {
   PrefService* prefs = profile ? profile->GetPrefs() : NULL;
   if (!prefs)
     return;
 
   bool pref_default = false;
 
   // Check the command-line/about:flags setting first, which should have
@@ skipping 165 matching lines @@
   GURL::Replacements replacements;
   replacements.SetSchemeStr(search_scheme);
   replacements.SetHostStr(search_host);
   replacements.SetPortStr(search_port);
   replacements.SetPathStr(search_path);
   return instant_url.ReplaceComponents(replacements);
 }
 
 }  // namespace search
 }  // namespace chrome