Adds a method to the Performance Monitor Database to fetch the most recent metric.

chrome/browser/performance_monitor/database.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/performance_monitor/database.h"
 
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/format_macros.h"
 #include "base/json/json_reader.h"
@@ skipping 361 matching lines @@
       start, static_cast<MetricType>(0), std::string());
   scoped_ptr<leveldb::Iterator> it(recent_db_->NewIterator(read_options_));
   for (it->Seek(start_key); it->Valid(); it->Next()) {
     RecentKey split_key = SplitRecentKey(it->key().ToString());
     if (split_key.type == metric_type)
       results.push_back(split_key.activity);
   }
   return results;
 }
 
+bool Database::GetRecentStatsForActivityAndMetric(
+    const std::string& activity,
+    MetricType metric,
+    MetricInfo* info) {
+  CHECK(!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+  std::string recent_map_key = CreateRecentMapKey(metric, activity);
+  if (!recent_map_.count(recent_map_key))
+    return false;
+  std::string recent_start_key = recent_map_[recent_map_key];

[eaugusti, 2012/07/31 18:46:06]

Not really a "start" key, just a key.

[chebert, 2012/07/31 19:26:36]

Done.

+
+  scoped_ptr<leveldb::Iterator> it(recent_db_->NewIterator(read_options_));

[eaugusti, 2012/07/31 18:46:06]

Maybe use Get() instead of an iterator:
http://leveldb.googlecode.com/svn/trunk/doc/index.html

You will have to check, but I think that it will return a status !s.ok() if the
key doesn't exist.

[chebert, 2012/07/31 19:26:36]

Done.

+
+  it->Seek(recent_start_key);
+  if (it->Valid()) {
+    RecentKey split_key = SplitRecentKey(it->key().ToString());
+    if (split_key.activity == activity) {
+      *info = MetricInfo(split_key.time, it->value().ToString());
+      return true;
+    }
+  }
+  return false;
+}
+
 Database::MetricInfoVector Database::GetStatsForActivityAndMetric(
     const std::string& activity, MetricType metric_type,
     const base::Time& start, const base::Time& end) {
   CHECK(!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   MetricInfoVector results;
   std::string start_key = CreateMetricKey(start, metric_type, activity);
   std::string end_key = CreateMetricKey(end, metric_type, activity);
   scoped_ptr<leveldb::Iterator> it(metric_db_->NewIterator(read_options_));
   for (it->Seek(start_key);
        it->Valid() && it->key().ToString() <= end_key;
@@ skipping 113 matching lines @@
     start_time_key_ = CreateActiveIntervalKey(current_time);
     end_time = start_time_key_;
   } else {
     end_time = CreateActiveIntervalKey(clock_->GetTime());
   }
   last_update_time_ = current_time;
   active_interval_db_->Put(write_options_, start_time_key_, end_time);
 }
 
 }  // namespace performance_monitor