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, 35 insertions, 0 deletions

diff --git a/src/build.h b/src/build.h
index c9ee4ac..4859c29 100644
--- a/src/build.h
+++ b/src/build.h
@@ -24,6 +24,7 @@
 using namespace std;
 
 #include "exit_status.h"
+#include "metrics.h"
 #include "util.h"  // int64_t
 
 struct BuildLog;
@@ -191,9 +192,43 @@ struct BuildStatus {
   /// The custom progress status format to use.
   const char* progress_status_format_;
 
+  struct RateInfo {
+    RateInfo() : last_update_(0), rate_(-1) {}
+
+    double rate() const { return rate_; }
+    int last_update() const { return last_update_; }
+    void Restart() { return stopwatch_.Restart(); }
+
+    double UpdateRate(int edges, int update_hint) {
+      if (update_hint != last_update_) {
+        rate_ = edges / stopwatch_.Elapsed() + 0.5;
+        last_update_ = update_hint;
+      }
+      return rate_;
+    }
+
+    template<class T>
+    void snprinfRate(T buf, const char* format) {
+      if (rate_ == -1)
+        snprintf(buf, sizeof(buf), "?");
+      else
+        snprintf(buf, sizeof(buf), format, rate_);
+    }
+
+  private:
+    Stopwatch stopwatch_;
+    int last_update_;
+    double rate_;
+  };
+
+  mutable RateInfo overall_rate_;
+  mutable RateInfo current_rate_;
+  const int current_rate_average_count_;
+
 #ifdef _WIN32
   void* console_;
 #endif
 };
 
 #endif  // NINJA_BUILD_H_
+