boost::chrono in mapnik timer impl

mapnik_timer.patch

diff --git a/include/mapnik/timer.hpp b/include/mapnik/timer.hpp
index 803f4d0..d7d7eb1 100644
--- a/include/mapnik/timer.hpp
+++ b/include/mapnik/timer.hpp
@@ -29,12 +29,49 @@
 #include <sstream>
 #include <iomanip>
 #include <ctime>
-#ifndef WIN32
-#include <sys/time.h> // for gettimeofday() on unix
+
+#if BOOST_VERSION >= 104700
+  #include <boost/chrono.hpp>
+  using boost::chrono;
+#else
+  #ifndef WIN32
+    #include <sys/time.h> // for gettimeofday() on unix
+    #include <sys/resource.h>
+  #else
+    #include <windows.h>
+  #endif
 #endif
 
+
 namespace mapnik {
 
+#if BOOST_VERSION >= 104700
+  typedef chrono::system_clock::time_point time_point_t;
+#else
+  typedef double time_point_t;
+#endif
+
+
+inline time_point_t time_now()
+{
+#if BOOST_VERSION >= 104700
+    return chrono::system_clock::now();
+#else
+  #ifndef WIN32
+    struct timeval t;
+    struct timezone tzp;
+    gettimeofday(&t, &tzp);
+    return t.tv_sec + t.tv_usec * 1e-6;
+  #else
+    LARGE_INTEGER t, f;
+    QueryPerformanceCounter(&t);
+    QueryPerformanceFrequency(&f);
+    return double(t.QuadPart) / double(f.QuadPart);
+  #endif
+#endif
+}
+
+
 // Measure times in both wall clock time and CPU times. Results are returned in milliseconds.
 class timer
 {
@@ -46,42 +83,48 @@ public:
 
     void restart()
     {
-        _stopped = false;
-        gettimeofday(&_wall_clock_start, NULL);
-        _cpu_start = clock();
+        stopped_ = false;
+        wall_clock_start_ = time_now();
+        cpu_start_ = clock();
     }
 
     virtual void stop() const
     {
-        _stopped = true;
-        _cpu_end = clock();
-        gettimeofday(&_wall_clock_end, NULL);
+        stopped_ = true;
+        cpu_end_ = clock();
+        wall_clock_end_ = time_now();
     }
 
     double cpu_elapsed() const
     {
         // return elapsed CPU time in ms
-        if (!_stopped)
+        if (! stopped_)
+        {
             stop();
+        }
 
-        return ((double) (_cpu_end - _cpu_start)) / CLOCKS_PER_SEC * 1000.0;
+        return ((double) (cpu_end_ - cpu_start_)) / CLOCKS_PER_SEC * 1000.0;
     }
 
     double wall_clock_elapsed() const
     {
         // return elapsed wall clock time in ms
-        if (!_stopped)
+        if (! stopped_)
+        {
             stop();
+        }
 
-        long seconds  = _wall_clock_end.tv_sec  - _wall_clock_start.tv_sec;
-        long useconds = _wall_clock_end.tv_usec - _wall_clock_start.tv_usec;
-
-        return ((seconds) * 1000 + useconds / 1000.0) + 0.5;
+#if BOOST_VERSION >= 104700
+        chrono::duration<double, chrono::milliseconds> ms = wall_clock_end_ - wall_clock_start_;
+        return ms.count();
+#else
+        return (wall_clock_end_ - wall_clock_start_) * 1000.0;
+#endif
     }
 protected:
-    mutable timeval _wall_clock_start, _wall_clock_end;
-    mutable clock_t _cpu_start, _cpu_end;
-    mutable bool _stopped;
+    mutable time_point_t wall_clock_start_, wall_clock_end_;
+    mutable clock_t cpu_start_, cpu_end_;
+    mutable bool stopped_;
 };
 
 //  A progress_timer behaves like a timer except that the destructor displays

does not compile for me. there are a few _stopped which appear to still need renaming to stopped_ and it looks like chrono::milliseconds needs to be boost::milli?

I just forked https://gist.github.com/2311987 with new diff that compiles for me.