Revert of SkTime::GetNSecs()

tools/timer/Timer.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef Timer_DEFINED
 #define Timer_DEFINED
 
+#include "SkTypes.h"
 #include "SkString.h"
-#include "SkTime.h"
-#include "SkTypes.h"
 
+#if defined(SK_BUILD_FOR_WIN32)
+    #include "SysTimer_windows.h"
+#elif defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS)
+    #include "SysTimer_mach.h"
+#elif defined(SK_BUILD_FOR_UNIX) || defined(SK_BUILD_FOR_ANDROID)
+    #include "SysTimer_posix.h"
+#endif
+
+#if SK_SUPPORT_GPU
+    #include "GpuTimer.h"
+#endif
+
+class SkGLContext;
+
+/**
+ * SysTimers and GpuTimers are implemented orthogonally.
+ * This class combines 2 SysTimers and a GpuTimer into one single,
+ * platform specific Timer with a simple interface. The truncated
+ * timer doesn't include the time required for the GPU to finish
+ * its rendering. It should always be <= the un-truncated system
+ * times and (for GPU configurations) can be used to roughly (very
+ * roughly) gauge the GPU load/backlog.
+ */
+class Timer {
+public:
+    explicit Timer(SkGLContext* gl = nullptr);
+
+    void start();
+    void truncatedEnd();
+    void end();
+
+    // All times in milliseconds.
+    double fCpu;
+    double fWall;
+    double fTruncatedCpu;
+    double fTruncatedWall;
+    double fGpu;
+
+private:
+    SysTimer fSysTimer;
+    SysTimer fTruncatedSysTimer;
+#if SK_SUPPORT_GPU
+    GpuTimer fGpuTimer;
+#endif
+};
+
+// Same as Timer above, supporting only fWall but with much lower overhead.
+// (Typically, ~30ns instead of Timer's ~1us.)
 class WallTimer {
 public:
-    WallTimer() : fWall(-1) {}
+    WallTimer();
 
-    void start() { fWall = SkTime::GetNSecs(); }
-    void end()   { fWall = (SkTime::GetNSecs() - fWall) * 1e-6; }
+    void start();
+    void end();
 
     double fWall;  // Milliseconds.
+
+private:
+    SysTimer fSysTimer;
 };
 
 SkString HumanizeMs(double);
 
 #endif