[fuchsia] Use FUCHSIA_AUDIO_NO_TIMESTAMP in AudioOutputStreamFuchsia

Previously AudioOutputStreamFuchsia was setting PTS (presentation
timestamp) to 0 to indicate that PTS is not set. The media_client API
expects FUCHSIA_AUDIO_NO_TIMESTAMP (!= 0) in that case.

Bug: 737802
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I858d72044f283f5bce1d457f7358644d6b258aa3
Reviewed-on: https://chromium-review.googlesource.com/801481Reviewed-by: James Robinson <jamesr@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520764}

media/audio/fuchsia/audio_output_stream_fuchsia.cc

@@ -133,14 +133,14 @@ void AudioOutputStreamFuchsia::PumpSamples() {
       audio_bus_->frames(), buffer_.data());
 
   do {
-    zx_time_t presentation_time = 0;
+    zx_time_t presentation_time = FUCHSIA_AUDIO_NO_TIMESTAMP;
     if (started_time_.is_null()) {
       // Presentation time (PTS) needs to be specified only for the first frame
       // after stream is started or restarted. Mixer will calculate PTS for all
       // following frames. 1us is added to account for the time passed between
       // zx_time_get() and fuchsia_audio_output_stream_write().
       zx_time_t zx_now = zx_time_get(ZX_CLOCK_MONOTONIC);
-      presentation_time = zx_now + presentation_delay_ns_ + 1000;
+      presentation_time = zx_now + presentation_delay_ns_ + ZX_USEC(1);
       started_time_ = base::TimeTicks::FromZxTime(zx_now);
       stream_position_samples_ = 0;
     }