Protector adds the default prepopulated engine if it was removed.

chrome/browser/protector/histograms.h

 // 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.
 
 #ifndef CHROME_BROWSER_PROTECTOR_HISTOGRAMS_H_
 #define CHROME_BROWSER_PROTECTOR_HISTOGRAMS_H_
 #pragma once
 
 class TemplateURL;
 
@@ skipping 19 matching lines @@
   // This is for convenience only, must always be the last.
   kProtectorErrorCount
 };
 
 // Histogram name to report the new default search provider.
 extern const char kProtectorHistogramNewSearchProvider[];
 // Histogram name to report when user accepts new default search provider.
 extern const char kProtectorHistogramSearchProviderApplied[];
 // Histogram name to report when user keeps previous default search provider.
 extern const char kProtectorHistogramSearchProviderDiscarded[];
+// Histogram name to report the fallback default search provider when the
+// backup value is invalid or doesn't match an existing provider.
+extern const char kProtectorHistogramSearchProviderFallback[];
+// Histogram name to report when the prepopulated default search provider was
+// missing and has been added for fallback.
+extern const char kProtectorHistogramSearchProviderMissing[];
+// Histogram name to report the default search provider restored by Protector
+// before showing user the bubble.
+extern const char kProtectorHistogramSearchProviderRestored[];
 // Histogram name to report when user ignores search provider change.
 extern const char kProtectorHistogramSearchProviderTimeout[];
 
 // Returns index to be used in histograms for given search provider (which may
 // be NULL, in which case a special index will be returned).
 int GetSearchProviderHistogramID(const TemplateURL* t_url);
 
 // Maximum value of search provider index in histogram enums.
 extern const int kProtectorMaxSearchProviderID;
 
 }  // namespace protector
 
 #endif  // CHROME_BROWSER_PROTECTOR_HISTOGRAMS_H_