Add unit tests for sub-components of CaptureScheduler.

remoting/base/rate_counter.h

 // Copyright (c) 2011 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.
 
-// RateCounter is defined to measure average rate over a given time window.
-// Rate is reported as the sum of values recorded divided by the time window.
-// This can be used for measuring bandwidth, bitrate, etc.
-
-// This class is thread-safe.
-
 #ifndef REMOTING_BASE_RATE_COUNTER_H_
 #define REMOTING_BASE_RATE_COUNTER_H_
 
 #include <queue>
 #include <utility>
 
 #include "base/basictypes.h"
-#include "base/synchronization/lock.h"
+#include "base/threading/non_thread_safe.h"
 #include "base/time.h"
 
 namespace remoting {
 
-class RateCounter {
+// Measures average rate per second of a sequence of point rate samples
+// over a specified time window. This can be used to measure bandwidth, frame
+// rates, etc.
+class RateCounter : public base::NonThreadSafe {
  public:
-  // Construct a counter for a specific time window.
-  RateCounter(base::TimeDelta time_window);
-
+  // Constructs a rate counter over the specified |time_window|.
+  explicit RateCounter(base::TimeDelta time_window);
   virtual ~RateCounter();
 
-  // Record the data point.
+  // Records a point event count to include in the rate.
   void Record(int64 value);
 
-  // Report the rate recorded. At the beginning of recording the numbers before
-  // |time_window| is reached the reported rate will not be accurate.
+  // Returns the rate-per-second of values recorded over the time window.
+  // Note that rates reported before |time_window| has elapsed are not accurate.
   double Rate();
 
+  // Overrides the current time for testing.
+  void SetCurrentTimeForTest(base::Time current_time);
+
  private:
-  // Helper function to evict old data points.
-  void Evict(base::Time current_time);
-
-  // A data point consists of a timestamp and a data value.
+  // Type used to store data points with timestamps.
   typedef std::pair<base::Time, int64> DataPoint;
 
-  // Duration of the time window.
-  base::TimeDelta time_window_;
+  // Removes data points more than |time_window| older than |current_time|.
+  void EvictOldDataPoints(base::Time current_time);
 
-  // Protects |data_points_| and |sum_|.
-  base::Lock lock_;
+  // Returns the current time specified for test, if set, or base::Time::Now().
+  base::Time CurrentTime() const;
 
-  // Keep the values of all the data points in a queue.
+  // Time window over which to calculate the rate.
+  const base::TimeDelta time_window_;
+
+  // Queue containing data points in the order in which they were recorded.
   std::queue<DataPoint> data_points_;
 
   // Sum of values in |data_points_|.
   int64 sum_;
 
+  // If set, used to calculate the running average, in place of Now().
+  base::Time current_time_for_test_;
+
   DISALLOW_COPY_AND_ASSIGN(RateCounter);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_BASE_RATE_COUNTER_H_