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

chrome/browser/performance_monitor/metric.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_METRIC_H_
 #define CHROME_BROWSER_PERFORMANCE_MONITOR_METRIC_H_
 
 #include <string>
 #include "base/time.h"
 
@@ skipping 14 matching lines @@
 METRIC_TEST_STARTUP_TIME,
 METRIC_SESSION_RESTORE_TIME,
 METRIC_PAGE_LOAD_TIME,
 METRIC_NETWORK_BYTES_READ,
 METRIC_NUMBER_OF_METRICS
 };
 
 struct Metric {
  public:
   Metric();
-  Metric(const base::Time& metric_time, const double metric_value);
-  Metric(const std::string& metric_time, const std::string& metric_value);
+  Metric(MetricType metric_type,
+         const base::Time& metric_time,
+         const double metric_value);
+  Metric(MetricType metric_type,
+         const std::string& metric_time,
+         const std::string& metric_value);
   ~Metric();
 
+  // Check the value in the metric to make sure that it is reasonable. Since
+  // some metric-gathering methods will fail and return incorrect values, we
+  // need to try to weed these out as best we can.
+  bool IsValid() const;
+
+  // This converts the double stored in value to a string format. This will
+  // not perform any checking on the validity of the metric, and only makes
+  // sense if the metric IsValid().
+  std::string ValueAsString() const;
+
+  MetricType type;
   base::Time time;
   double value;
 };
 
 }  // namespace performance_monitor
 
 #endif  // CHROME_BROWSER_PERFORMANCE_MONITOR_METRIC_H_