Revert of SkTime updates

src/core/SkTime.cpp

Index: src/core/SkTime.cpp
diff --git a/src/core/SkTime.cpp b/src/core/SkTime.cpp
index 16f66161a78969d6bea59644a30d7ed43d30ef88..86a0685c70af27703490024f15bf80ff5aef5152 100644
--- a/src/core/SkTime.cpp
+++ b/src/core/SkTime.cpp
@@ -36,13 +36,24 @@
             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();
     }