Use rtc::time for all your timing needs!

Initial step of unifying so that base/timeutils.h and Clock/TimeTime
from system_wrappers use the same implementation.

BUG=webrtc:5463
R=pbos@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1639543005 .

Cr-Commit-Position: refs/heads/master@{#11394}

webrtc/base/timeutils.cc

@@ -74,6 +74,8 @@ uint64_t TimeNanos() {
   // TODO: Calculate with nanosecond precision.  Otherwise, we're just
   // wasting a multiply and divide when doing Time() on Windows.
   ticks = ticks * kNumNanosecsPerMillisec;
+#else
+#error Unsupported platform.
 #endif
   return ticks;
 }