[Fuchsia] Fix Play() and SendPacket() order in AudioOutputStreamFuchsia

Two fixes for AudioOutputStreamFuchsia:
 - Don't call Play() until after the first SendPacket() call as is
   required by the AudioRenderer interface.
 - Add padding to min_lead_time_ for the first packet, to reduce the
   chance that samples at the beginning of the stream are dropped.

Bug: 974029
Change-Id: If2dc43a3df7d671a42f7983dea130fa3b10ad1ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1659230
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669914}

media/audio/fuchsia/audio_output_stream_fuchsia.cc

@@ -197,7 +197,8 @@ void AudioOutputStreamFuchsia::PumpSamples() {
 
   base::TimeDelta delay;
   if (reference_time_.is_null()) {
-    delay = min_lead_time_.value();
+    delay = min_lead_time_.value() + parameters_.GetBufferDuration() / 2;
+    stream_position_samples_ = 0;
   } else {
     auto stream_time = GetCurrentStreamTime();
 
@@ -211,14 +212,6 @@ void AudioOutputStreamFuchsia::PumpSamples() {
     delay = stream_time - now;
   }
 
-  // Start playback if the stream was previously stopped.
-  if (reference_time_.is_null()) {
-    stream_position_samples_ = 0;
-    reference_time_ = now + min_lead_time_.value();
-    audio_renderer_->PlayNoReply(reference_time_.ToZxTime(),
-                                 stream_position_samples_);
-  }
-
   // Request more samples from |callback_|.
   int frames_filled = callback_->OnMoreData(delay, now, 0, audio_bus_.get());
   DCHECK_EQ(frames_filled, audio_bus_->frames());
@@ -242,6 +235,13 @@ void AudioOutputStreamFuchsia::PumpSamples() {
   packet.flags = 0;
   audio_renderer_->SendPacketNoReply(std::move(packet));
 
+  // Start playback if the stream was previously stopped.
+  if (reference_time_.is_null()) {
+    reference_time_ = now + delay;
+    audio_renderer_->PlayNoReply(reference_time_.ToZxTime(),
+                                 stream_position_samples_);
+  }
+
   stream_position_samples_ += frames_filled;
   payload_buffer_pos_ =
       (payload_buffer_pos_ + packet_size) % payload_buffer_.size();