[Fuchsia] Add missing includes in Fuchsia-specific files.

1. media/audio/fuchsia/audio_output_stream_fuchsia.cc uses
   zx_get_time(), so it must include zircon/syscalls.h
2. mojo/edk/system/channel_fuchsia.cc uses ScopedZxHandle, so it must
   include base/fuchsia/scoped_zx_handle.h

Change-Id: I0155c24d849f7736f3f678a862248c70bd058449
Reviewed-on: https://chromium-review.googlesource.com/986978
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547000}

media/audio/fuchsia/audio_output_stream_fuchsia.cc

@@ -5,6 +5,7 @@
 #include "media/audio/fuchsia/audio_output_stream_fuchsia.h"
 
 #include <media/audio.h>
+#include <zircon/syscalls.h>
 
 #include "media/audio/fuchsia/audio_manager_fuchsia.h"
 #include "media/base/audio_sample_types.h"

mojo/edk/system/channel_fuchsia.cc

@@ -14,6 +14,7 @@
 #include "base/bind.h"
 #include "base/containers/circular_deque.h"
 #include "base/files/scoped_file.h"
+#include "base/fuchsia/scoped_zx_handle.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"