Fix the chain that propagates the audio frame's rtp and ntp timestamp including:
* In AudioCodingModuleImpl::PlayoutData10Ms, don't reset the timestamp got from GetAudio.
* When there're more than one participant, set AudioFrame's RTP timestamp to 0.
* Copy ntp_time_ms_ in AudioFrame::CopyFrom method.
* In RemixAndResample, pass src frame's timestamp_ and ntp_time_ms_ to the dst frame.
* Fix how |elapsed_time_ms| is computed in channel.cc by adding GetPlayoutFrequency.

Tweaks on ntp_time_ms_:
* Init ntp_time_ms_ to -1 in AudioFrame ctor.
* When there're more than one participant, set AudioFrame's ntp_time_ms_ to an invalid value. I.e. we don't support ntp_time_ms_ in multiple participants case before the mixing is moved to chrome.

Added elapsed_time_ms to AudioFrame and pass it to chrome, where we don't have the information about the rtp timestmp's sample rate, i.e. can't convert rtp timestamp to ms.

BUG=3111
R=henrik.lundin@webrtc.org, turaj@webrtc.org, xians@webrtc.org
TBR=andrew
andrew to take another look on audio_conference_mixer_impl.cc

Review URL: https://webrtc-codereview.appspot.com/14559004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6346 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/talk/app/webrtc/test/fakeaudiocapturemodule_unittest.cc b/talk/app/webrtc/test/fakeaudiocapturemodule_unittest.cc
index ea92f7b..ab0db06 100644
--- a/talk/app/webrtc/test/fakeaudiocapturemodule_unittest.cc
+++ b/talk/app/webrtc/test/fakeaudiocapturemodule_unittest.cc
@@ -86,7 +86,7 @@
                                    void* audioSamples,
 #ifdef USE_WEBRTC_DEV_BRANCH
                                    uint32_t& nSamplesOut,
-                                   uint32_t* rtp_timestamp,
+                                   int64_t* elapsed_time_ms,
                                    int64_t* ntp_time_ms) {
 #else
                                    uint32_t& nSamplesOut) {
@@ -98,7 +98,7 @@
         GenerateZeroBuffer(audioSamples, audio_buffer_size);
     nSamplesOut = bytes_out / nBytesPerSample;
 #ifdef USE_WEBRTC_DEV_BRANCH
-    *rtp_timestamp = 0;
+    *elapsed_time_ms = 0;
     *ntp_time_ms = 0;
 #endif
     return 0;