print edges per second

prints the rate of finished edges per second to the console,
for instance with NINJA_STATUS="[%s/%t %o(%c)/s] ":

[132/1922 16.1(14)/s]

16.1 is the average for all processed files (here 132 since start)
14 is the average of the last n files while n is the number specifies by
-j (or its default)

1 files changed, 25 insertions, 0 deletions

diff --git a/src/metrics.h b/src/metrics.h
index af6e9a2..dae6b9f 100644
--- a/src/metrics.h
+++ b/src/metrics.h
@@ -33,6 +33,7 @@ struct Metric {
   int64_t sum;
 };
 
+
 /// A scoped object for recording a metric across the body of a function.
 /// Used by the METRIC_RECORD macro.
 struct ScopedMetric {
@@ -57,6 +58,30 @@ private:
   vector<Metric*> metrics_;
 };
 
+/// Get the current time as relative to some epoch.
+/// Epoch varies between platforms; only useful for measuring elapsed
+/// time.
+int64_t GetTimeMillis();
+
+
+/// A simple stopwatch which retruns the time
+// in seconds since Restart() was called
+class Stopwatch
+{
+public:
+  Stopwatch() : started_(0) {}
+
+  /// Seconds since Restart() call
+  double Elapsed() const { return 1e-6 * (Now() - started_); }
+
+  void Restart() { started_ = Now(); }
+
+private:
+  uint64_t started_;
+  uint64_t Now() const;
+};
+
+
 /// The primary interface to metrics.  Use METRIC_RECORD("foobar") at the top
 /// of a function to get timing stats recorded for each call of the function.
 #define METRIC_RECORD(name)                                             \