[protector] Added UI for invalid Preferences backup case.

chrome/browser/protector/protected_prefs_watcher.cc

 // Copyright (c) 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/protector/protected_prefs_watcher.h"
 
 #include "base/base64.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/stringprintf.h"
@@ skipping 214 matching lines @@
         kProtectorHistogramPrefs,
         kProtectorErrorValueValidZero,
         kProtectorErrorCount);
   } else if (IsSignatureValid()) {
     UMA_HISTOGRAM_ENUMERATION(
         kProtectorHistogramPrefs,
         kProtectorErrorValueValid,
         kProtectorErrorCount);
   } else {
     LOG(WARNING) << "Invalid backup signature";
-    // Further changes to protected prefs will overwrite the signature.
     is_backup_valid_ = false;
+    // The whole backup has been compromised, overwrite it.
+    InitBackup();
     UMA_HISTOGRAM_ENUMERATION(
         kProtectorHistogramPrefs,
         kProtectorErrorBackupInvalid,
         kProtectorErrorCount);
   }
 }
 
 std::string ProtectedPrefsWatcher::GetSignatureData(PrefService* prefs) const {
   // std::stringstream data;
   std::string data = base::StringPrintf(
@@ skipping 15 matching lines @@
   // a consistent (sorted) order.
   for (ExtensionPrefs::ExtensionIdSet::const_iterator it =
            cached_extension_ids_.begin();
        it != cached_extension_ids_.end(); ++it) {
     base::StringAppendF(&data, "|%s", it->c_str());
   }
   return data;
 }
 
 }  // namespace protector