Revert of SkTime updates

src/core/SkTime.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkOncePtr.h"
 #include "SkString.h"
 #include "SkTime.h"
@@ skipping 18 matching lines @@
     #include <intrin.h>
     SK_DECLARE_STATIC_ONCE_PTR(double, ns_per_tick);
     double SkTime::GetNSecs() {
         uint64_t ticks = __rdtsc();
         return ticks * *ns_per_tick.get([]{
             LARGE_INTEGER khz;  // The docs say this returns Hz, but it returns KHz.
             QueryPerformanceFrequency(&khz);
             return new double(1e6 / khz.QuadPart);
         });
     }
+#elif defined(__MACH__)
+    // TODO: fold into std::chrono when available?
+    #include <mach/mach_time.h>
+    SK_DECLARE_STATIC_ONCE_PTR(double, ns_per_tick);
+    double SkTime::GetNSecs() {
+        uint64_t ticks = mach_absolute_time();
+        return ticks * *ns_per_tick.get([]{
+            mach_timebase_info_data_t timebase;
+            (void)mach_timebase_info(&timebase);
+            return new double(timebase.numer * 1.0 / timebase.denom);
+        });
+    }
 #else
-    // This std::chrono code looks great on Linux, Mac, and Android,
-    // but MSVC 2013 returns mostly garbage (0ns times, etc).
-    // This is ostensibly fixed in MSVC 2015.
+    // This std::chrono code looks great on Linux and Android,
+    // but MSVC 2013 returned mostly garbage (0ns times, etc).
     #include <chrono>
     double SkTime::GetNSecs() {
-        auto now = std::chrono::steady_clock::now();
+        auto now = std::chrono::high_resolution_clock::now();
         std::chrono::duration<double, std::nano> ns = now.time_since_epoch();
         return ns.count();
     }
 #endif