Always execute FakeAudioWorker::|worker_cb_| even if late.

Most output clients are expecting that |worker_cb_| will consume N
frames and that subsequently the clock advances by N frames. Not
calling the |worker_cb_| stalls these internal clocks.

There's still the issue that tasks are incredibly delayed in the
ScopedTaskEnvironment on macOS. I.e., playback will still be slower than
realtime, but it at least won't be 0.25x as we spend forever trying to
catch up before executing the callback.

BUG=1003761,1014646
R=miu

Change-Id: Iaa98d683ba77fa664f13da2436cb69bf834251ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1898641
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715430}

media/audio/fake_audio_output_stream.cc

@@ -69,8 +69,9 @@ void FakeAudioOutputStream::CallOnMoreData(base::TimeTicks ideal_time,
   DCHECK(audio_manager_->GetWorkerTaskRunner()->BelongsToCurrentThread());
   // Real streams provide small tweaks to their delay values, alongside the
   // current system time; and so the same is done here.
-  callback_->OnMoreData(fixed_data_delay_ + (ideal_time - now), now, 0,
-                        audio_bus_.get());
+  const auto delay =
+      fixed_data_delay_ + std::max(base::TimeDelta(), ideal_time - now);
+  callback_->OnMoreData(delay, now, 0, audio_bus_.get());
 }
 
 void FakeAudioOutputStream::SetMute(bool muted) {}

media/base/fake_audio_worker.cc

@@ -166,9 +166,12 @@ void FakeAudioWorker::Worker::DoRead() {
     base::AutoLock scoped_lock(worker_cb_lock_);
     // Important to sample the clock after waiting to acquire the lock.
     now = base::TimeTicks::Now();
-    if (worker_cb_ && next_read_time > now) {
+
+    // Note: Even if we're late, this callback must be called. In many cases we
+    // are driving an underlying "samples consumed" based clock with these
+    // calls.
+    if (worker_cb_)
       worker_cb_.Run(read_time, now);
-    }
   }
 
   // If we're behind, find the next nearest ontime interval. Note, we could be