Change Timing::WallTimeNow to be static.

There's no need to construct a Timing object to call this method.
On Windows we were unnecessarily calling CreateWaitableTimer + CloseHandle but never actually using that waitable timer.

There's otherwise no change in functionality.

R=xians@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/20869004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@6624 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/base/timing.cc b/base/timing.cc
index aa1fc42..0c5ed5e 100644
--- a/base/timing.cc
+++ b/base/timing.cc
@@ -46,6 +46,7 @@
 #endif
 }
 
+// static
 double Timing::WallTimeNow() {
 #if defined(WEBRTC_POSIX)
   struct timeval time;
diff --git a/base/timing.h b/base/timing.h
index 58b17a9..1dee607 100644
--- a/base/timing.h
+++ b/base/timing.h
@@ -24,7 +24,8 @@
 
   // WallTimeNow() returns the current wall-clock time in seconds,
   // within 10 milliseconds resolution.
-  virtual double WallTimeNow();
+  // WallTimeNow is static and does not require a timer_handle_ on Windows.
+  static double WallTimeNow();
 
   // TimerNow() is like WallTimeNow(), but is monotonically
   // increasing.  It returns seconds in resolution of 10 microseconds