Add SetAudioPlayout and SetAudioRecording methods to the PeerConnection API (II)

Second attempt to land https://webrtc-review.googlesource.com/c/src/+/16180

Now removes voice_engine dependency from peerconnection and fixes a minor
const issue in NullAudioPoller.

TBR=solenberg

Bug: webrtc:7313
Change-Id: Ibfddbdc76118581e4a4dc64575203f84c1659e5c
Reviewed-on: https://webrtc-review.googlesource.com/17784
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Commit-Queue: Henrik Andreassson <henrika@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20526}
diff --git a/audio/null_audio_poller.cc b/audio/null_audio_poller.cc
new file mode 100644
index 0000000..c22b3d8
--- /dev/null
+++ b/audio/null_audio_poller.cc
@@ -0,0 +1,66 @@
+/*
+ *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "audio/null_audio_poller.h"
+#include "rtc_base/logging.h"
+#include "rtc_base/thread.h"
+
+namespace webrtc {
+namespace internal {
+
+namespace {
+
+constexpr int64_t kPollDelayMs = 10;  // WebRTC uses 10ms by default
+
+constexpr size_t kNumChannels = 1;
+constexpr uint32_t kSamplesPerSecond = 48000;            // 48kHz
+constexpr size_t kNumSamples = kSamplesPerSecond / 100;  // 10ms of samples
+
+}  // namespace
+
+NullAudioPoller::NullAudioPoller(AudioTransport* audio_transport)
+    : audio_transport_(audio_transport),
+      reschedule_at_(rtc::TimeMillis() + kPollDelayMs) {
+  RTC_DCHECK(audio_transport);
+  OnMessage(nullptr);  // Start the poll loop.
+}
+
+NullAudioPoller::~NullAudioPoller() {
+  RTC_DCHECK(thread_checker_.CalledOnValidThread());
+  rtc::Thread::Current()->Clear(this);
+}
+
+void NullAudioPoller::OnMessage(rtc::Message* msg) {
+  RTC_DCHECK(thread_checker_.CalledOnValidThread());
+
+  // Buffer to hold the audio samples.
+  int16_t buffer[kNumSamples * kNumChannels];
+  // Output variables from |NeedMorePlayData|.
+  size_t n_samples;
+  int64_t elapsed_time_ms;
+  int64_t ntp_time_ms;
+  audio_transport_->NeedMorePlayData(kNumSamples, sizeof(int16_t), kNumChannels,
+                                     kSamplesPerSecond, buffer, n_samples,
+                                     &elapsed_time_ms, &ntp_time_ms);
+
+  // Reschedule the next poll iteration. If, for some reason, the given
+  // reschedule time has already passed, reschedule as soon as possible.
+  int64_t now = rtc::TimeMillis();
+  if (reschedule_at_ < now) {
+    reschedule_at_ = now;
+  }
+  rtc::Thread::Current()->PostAt(RTC_FROM_HERE, reschedule_at_, this, 0);
+
+  // Loop after next will be kPollDelayMs later.
+  reschedule_at_ += kPollDelayMs;
+}
+
+}  // namespace internal
+}  // namespace webrtc