Add guards to metric values; erase bad events/metrics from db

chrome/browser/performance_monitor/constants.h

 // 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.
 
 #ifndef CHROME_BROWSER_PERFORMANCE_MONITOR_CONSTANTS_H_
 #define CHROME_BROWSER_PERFORMANCE_MONITOR_CONSTANTS_H_
 
+#include "base/basictypes.h"
+
 namespace performance_monitor {
 
 // Constants which are used by the PerformanceMonitor and its related classes.
 // The constants should be documented alongside the definition of their values
 // in the .cc file.
 
 extern const char kMetricNotFoundError[];
 extern const char kProcessChromeAggregate[];
 extern const int kDefaultGatherIntervalInSeconds;
 
 // State tokens
 extern const char kStateChromeVersion[];
 extern const char kStateProfilePrefix[];
 
+// Unit values (for use in metric, and on the UI side).
+
+// Memory measurements
+extern const int64 kBytesPerKilobyte;
+extern const int64 kBytesPerMegabyte;
+extern const int64 kBytesPerGigabyte;
+extern const int64 kBytesPerTerabyte;
+
+// Time measurements - Most of these are imported from base/time.h
+// These units are used for display (and it's related calculations), not for
+// any mathematical analysis. Thus we can estimate for values without an exact
+// conversion.
+extern const int64 kMicrosecondsPerMonth;
+extern const int64 kMicrosecondsPerYear;
+
 }  // namespace performance_monitor
 
 #endif  // CHROME_BROWSER_PERFORMANCE_MONITOR_CONSTANTS_H_