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

chrome/browser/performance_monitor/performance_monitor.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_PERFORMANCE_MONITOR_H_
 #define CHROME_BROWSER_PERFORMANCE_MONITOR_PERFORMANCE_MONITOR_H_
 
 #include <map>
 #include <string>
 
@@ skipping 113 matching lines @@
   // Check the previous Chrome version from the Database and determine if
   // it has been updated. If it has, insert an event in the database.
   void CheckForVersionUpdateOnBackgroundThread();
 
   // Wrapper function for inserting events into the database.
   void AddEvent(scoped_ptr<Event> event);
 
   void AddEventOnBackgroundThread(scoped_ptr<Event> event);
 
   // Since Database::AddMetric() is overloaded, base::Bind() does not work and
-  // we need a helper function.
-  void AddMetricOnBackgroundThread(MetricType type, const std::string& value);
+  // we need a helper function. Deliberately not const & so that we will
+  // construct a new metric on the background thread.

[Yoyo Zhou, 2012/09/10 23:52:44]

I'm not sure this does what you think. You are still constructing Metric where
you post the callback, and then making a copy of it, if I understand correctly.

[Devlin, 2012/09/11 18:52:17]

I was modeling this after the io_data one. In that, Battre recommended I pass in
a copy, rather than a const ref, so that it would be thread-safe (see here:
https://chromiumcodereview.appspot.com/10829342/diff2/9003:10007/chrome/brows...
). I think that a const& would be safe here so long as we always construct the
Metric in the call (and the callback owns it), but would it still be safe if we
did:

Metric metric(...);
base::Bind(..., metric)

or would PerformanceMonitor's thread still own it?

[Yoyo Zhou, 2012/09/13 00:09:20]

On reviewing the documentation in callback.h, this looks correct. Sorry for the
confusion.

+  void AddMetricOnBackgroundThread(Metric metric);
 
   // Notify any listeners that PerformanceMonitor has finished the initializing.
   void NotifyInitialized();
 
   // Perform any collections that are done on a timed basis.
   void DoTimedCollections();
 
   // Update the database record of the last time the active profiles were
   // running; this is used in determining when an unclean exit occurred.
   void UpdateLiveProfiles();
@@ skipping 55 matching lines @@
   // the PERFORMANCE_MONITOR_INITIALIZED notification or should check this
   // flag.
   static bool initialized_;
 
   DISALLOW_COPY_AND_ASSIGN(PerformanceMonitor);
 };
 
 }  // namespace performance_monitor
 
 #endif  // CHROME_BROWSER_PERFORMANCE_MONITOR_PERFORMANCE_MONITOR_H_