Added a timer-based report to the metrics library.

Timer encapsulates a timer with basic functionality.
TimerReporter subclasses it for also sending UMA reports.

BUG=chromium-os:18800
TEST=Unit test 'timer_test' has been included

Change-Id: I9de9a2a7388721ba1476fe706a8d12788d2176ad
Reviewed-on: http://gerrit.chromium.org/gerrit/5161
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Bruno Pontes Soares Rocha <bpontes@google.com>
Reviewed-by: Bruno Pontes Soares Rocha <bpontes@google.com>
diff --git a/metrics/timer.cc b/metrics/timer.cc
new file mode 100644
index 0000000..67b0fd1
--- /dev/null
+++ b/metrics/timer.cc
@@ -0,0 +1,77 @@
+// Copyright (c) 2011 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.
+
+#include "timer.h"
+
+#include <string>
+
+#include <base/memory/scoped_ptr.h>
+#include <base/time.h>
+
+#include "metrics_library.h"
+
+namespace chromeos_metrics {
+
+base::TimeTicks ClockWrapper::GetCurrentTime() const {
+  return base::TimeTicks::Now();
+}
+
+Timer::Timer()
+    : is_started_(false),
+      clock_wrapper_(new ClockWrapper()) {}
+
+bool Timer::Start() {
+  start_time_ = clock_wrapper_->GetCurrentTime();
+  is_started_ = true;
+  return true;
+}
+
+bool Timer::Stop() {
+  // Check if the timer has been started.
+  if (!is_started_) return false;
+  is_started_ = false;
+  elapsed_time_ = clock_wrapper_->GetCurrentTime() - start_time_;
+  return true;
+}
+
+bool Timer::Reset() {
+  is_started_ = false;
+  return true;
+}
+
+bool Timer::HasStarted() const {
+  return is_started_;
+}
+
+bool Timer::GetElapsedTime(base::TimeDelta* elapsed_time) const {
+  if (start_time_.is_null() || !elapsed_time) return false;
+  if (is_started_) {
+    *elapsed_time = clock_wrapper_->GetCurrentTime() - start_time_;
+  } else {
+    *elapsed_time = elapsed_time_;
+  }
+  return true;
+}
+
+// static
+MetricsLibraryInterface* TimerReporter::metrics_lib_ = NULL;
+
+TimerReporter::TimerReporter(const std::string& histogram_name, int min,
+                             int max, int num_buckets)
+    : histogram_name_(histogram_name),
+      min_(min),
+      max_(max),
+      num_buckets_(num_buckets) {}
+
+bool TimerReporter::ReportMilliseconds() const {
+  base::TimeDelta elapsed_time;
+  if (!metrics_lib_ || !GetElapsedTime(&elapsed_time)) return false;
+  return metrics_lib_->SendToUMA(histogram_name_,
+                                 elapsed_time.InMilliseconds(),
+                                 min_,
+                                 max_,
+                                 num_buckets_);
+}
+
+}  // namespace chromeos_metrics