Revert of SkTime::GetNSecs()

tools/timer/SysTimer_windows.cpp

+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "SysTimer_windows.h"
+
+#include <intrin.h>
+
+static ULONGLONG win_cpu_time() {
+    FILETIME createTime;
+    FILETIME exitTime;
+    FILETIME usrTime;
+    FILETIME sysTime;
+    if (0 == GetProcessTimes(GetCurrentProcess(), &createTime, &exitTime, &sysTime, &usrTime)) {
+        return 0;
+    }
+    ULARGE_INTEGER start_cpu_sys;
+    ULARGE_INTEGER start_cpu_usr;
+    start_cpu_sys.LowPart  = sysTime.dwLowDateTime;
+    start_cpu_sys.HighPart = sysTime.dwHighDateTime;
+    start_cpu_usr.LowPart  = usrTime.dwLowDateTime;
+    start_cpu_usr.HighPart = usrTime.dwHighDateTime;
+    return start_cpu_sys.QuadPart + start_cpu_usr.QuadPart;
+}
+
+void SysTimer::startCpu() {
+    fStartCpu = win_cpu_time();
+}
+
+double SysTimer::endCpu() {
+    ULONGLONG end_cpu = win_cpu_time();
+    return static_cast<double>(end_cpu - fStartCpu) / 10000.0L;
+}
+
+// On recent Intel chips (roughly, "has Core or Atom in its name") __rdtsc will always tick
+// at the CPU's maximum rate, even while power management clocks the CPU up and down.
+// That's great, because it makes measuring wall time super simple.
+
+void SysTimer::startWall() {
+    fStartWall = __rdtsc();
+}
+
+double SysTimer::endWall() {
+    unsigned __int64 end = __rdtsc();
+
+    // This seems to, weirdly, give the CPU frequency in kHz.  That's exactly what we want!
+    LARGE_INTEGER freq_khz;
+    QueryPerformanceFrequency(&freq_khz);
+
+    return static_cast<double>(end - fStartWall) / static_cast<double>(freq_khz.QuadPart);
+}