[Cast] In Audio/VideoSender, drop frames when too-long a duration is in-flight.

media/cast/sender/rtp_timestamp_helper.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/cast/sender/rtp_timestamp_helper.h"
 
+#include "media/cast/cast_defines.h"
+
 namespace media {
 namespace cast {
 
 RtpTimestampHelper::RtpTimestampHelper(int frequency)
     : frequency_(frequency),
       last_rtp_timestamp_(0) {
 }
 
 RtpTimestampHelper::~RtpTimestampHelper() {
 }
 
-bool RtpTimestampHelper::GetCurrentTimeAsRtpTimestamp(
-    const base::TimeTicks& now, uint32* rtp_timestamp) const {
+bool RtpTimestampHelper::EstimateRtpTimestamp(
+    const base::TimeTicks& t, uint32* rtp_timestamp) const {
   if (last_capture_time_.is_null())
     return false;
-  const base::TimeDelta elapsed_time = now - last_capture_time_;
-  const int64 rtp_delta =
-      elapsed_time * frequency_ / base::TimeDelta::FromSeconds(1);
+  const base::TimeDelta elapsed_time = t - last_capture_time_;
+  const int64 rtp_delta = TimeDeltaToRtpDelta(elapsed_time, frequency_);
   *rtp_timestamp = last_rtp_timestamp_ + static_cast<uint32>(rtp_delta);
   return true;
 }
 
 void RtpTimestampHelper::StoreLatestTime(
     base::TimeTicks capture_time, uint32 rtp_timestamp) {
   last_capture_time_ = capture_time;
   last_rtp_timestamp_ = rtp_timestamp;
 }
 
 }  // namespace cast
 }  // namespace media