Replace Clock::CurrentNtp with Clock::CurrentNtpTime

CurrentNtp return time by taking two output parameters by reference
(also breaks style guide)
CurrentNtpTime treat ntp time as single entity and returns it using NtpTime structure.
(making interface clearer)

BUG=None

Review-Url: https://codereview.webrtc.org/2733823002
Cr-Commit-Position: refs/heads/master@{#17088}

webrtc/test/drifting_clock.cc

diff --git a/webrtc/test/drifting_clock.cc b/webrtc/test/drifting_clock.cc
index 76f1723..b110776 100644
--- a/webrtc/test/drifting_clock.cc
+++ b/webrtc/test/drifting_clock.cc
@@ -39,15 +39,14 @@
   return clock_->TimeInMicroseconds() + Drift();
 }
 
-void DriftingClock::CurrentNtp(uint32_t& seconds, uint32_t& fractions) const {
+NtpTime DriftingClock::CurrentNtpTime() const {
   // NTP precision is 1/2^32 seconds, i.e. 2^32 ntp fractions = 1 second.
   const double kNtpFracPerMicroSecond = 4294.967296;  // = 2^32 / 10^6
 
-  clock_->CurrentNtp(seconds, fractions);
-  uint64_t total_fractions = (static_cast<uint64_t>(seconds) << 32) | fractions;
+  NtpTime ntp = clock_->CurrentNtpTime();
+  uint64_t total_fractions = static_cast<uint64_t>(ntp);
   total_fractions += Drift() * kNtpFracPerMicroSecond;
-  seconds = total_fractions >> 32;
-  fractions = static_cast<uint32_t>(total_fractions);
+  return NtpTime(total_fractions);
 }
 
 int64_t DriftingClock::CurrentNtpInMilliseconds() const {