Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data.Linq/SqlClient/PerfTimer.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading;
+
+namespace System.Data.Linq.SqlClient {
+#if PERFORMANCE_BUILD
+    class PerfTimer {
+        long startTime;
+        long stopTime;
+        long frequency;
+
+        public PerfTimer() {
+            QueryPerformanceFrequency(out frequency);
+        }
+
+        public void Start() {
+            Thread.Sleep(0);
+            QueryPerformanceCounter(out startTime);
+        }
+
+        public void Stop() {
+            QueryPerformanceCounter(out stopTime);
+        }
+
+        public long Duration {
+            get { return (long)( 1000000.0 * (double)(stopTime - startTime) / (double) frequency ); }
+        }
+
+        [System.Runtime.InteropServices.DllImport("Kernel32.dll")]
+        private static extern bool QueryPerformanceCounter(out long count);
+
+        [System.Runtime.InteropServices.DllImport("Kernel32.dll")]
+        private static extern bool QueryPerformanceFrequency(out long frequency);
+    }
+#endif
+}