diff --git a/prefs.cc b/prefs.cc
index 067f768..cb6e4f7 100644
--- a/prefs.cc
+++ b/prefs.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -33,6 +33,8 @@
 const char kPrefsUpdateStateSignatureBlob[] = "update-state-signature-blob";
 const char kPrefsUpdateStateSignedSHA256Context[] =
     "update-state-signed-sha-256-context";
+const char kPrefsUpdateCheckCount[] = "update-check-count";
+const char kPrefsWallClockWaitPeriod[] = "wall-clock-wait-period";
 
 bool Prefs::Init(const FilePath& prefs_dir) {
   prefs_dir_ = prefs_dir;
@@ -43,8 +45,6 @@
   FilePath filename;
   TEST_AND_RETURN_FALSE(GetFileNameForKey(key, &filename));
   if (!file_util::ReadFileToString(filename, value)) {
-    PLOG(INFO) << "Unable to read prefs from " << filename.value()
-               << ". This is likely harmless.";
     return false;
   }
   return true;
@@ -72,6 +72,18 @@
   return SetString(key, base::Int64ToString(value));
 }
 
+bool Prefs::Exists(const string& key) {
+  FilePath filename;
+  TEST_AND_RETURN_FALSE(GetFileNameForKey(key, &filename));
+  return file_util::PathExists(filename);
+}
+
+bool Prefs::Delete(const string& key) {
+  FilePath filename;
+  TEST_AND_RETURN_FALSE(GetFileNameForKey(key, &filename));
+  return file_util::Delete(filename, false);
+}
+
 bool Prefs::GetFileNameForKey(const std::string& key, FilePath* filename) {
   // Allows only non-empty keys containing [A-Za-z0-9_-].
   TEST_AND_RETURN_FALSE(!key.empty());