Fixing audio timestamp stall during inactivation (under a kill switch)

TEST: tested on chromium.

(cherry picked from commit 49dbad0)

No-Try: True
Bug: webrtc:12397, chromium:1171206
Change-Id: I1e15605f90e253a6ef61ab7ead8c576a80e8f01b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/203886
Reviewed-by: Jakob Ivarsson <[email protected]>
Reviewed-by: Harald Alvestrand <[email protected]>
Reviewed-by: Sam Zackrisson <[email protected]>
Commit-Queue: Minyue Li <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#33080}
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/204302
Reviewed-by: Mirko Bonadei <[email protected]>
Reviewed-by: Minyue Li <[email protected]>
Cr-Commit-Position: refs/branch-heads/4389@{#4}
Cr-Branched-From: 7acc2d9-refs/heads/master@{#32986}

audio/channel_send.cc

@@ -241,6 +241,8 @@ class ChannelSend : public ChannelSendInterface,
   // Defined last to ensure that there are no running tasks when the other
   // members are destroyed.
   rtc::TaskQueue encoder_queue_;
+
+  const bool fixing_timestamp_stall_;
 };
 
 const int kTelephoneEventAttenuationdB = 10;
@@ -471,7 +473,9 @@ ChannelSend::ChannelSend(
       crypto_options_(crypto_options),
       encoder_queue_(task_queue_factory->CreateTaskQueue(
           "AudioEncoder",
-          TaskQueueFactory::Priority::NORMAL)) {
+          TaskQueueFactory::Priority::NORMAL)),
+      fixing_timestamp_stall_(
+          !field_trial::IsDisabled("WebRTC-Audio-FixTimestampStall")) {
   RTC_DCHECK(module_process_thread);
   module_process_thread_checker_.Detach();
 
@@ -808,6 +812,10 @@ void ChannelSend::ProcessAndEncodeAudio(
       [this, audio_frame = std::move(audio_frame)]() mutable {
         RTC_DCHECK_RUN_ON(&encoder_queue_);
         if (!encoder_queue_is_active_) {
+          if (fixing_timestamp_stall_) {
+            _timeStamp +=
+                static_cast<uint32_t>(audio_frame->samples_per_channel_);
+          }
           return;
         }
         // Measure time between when the audio frame is added to the task queue