Revert 282424 "Remove media::AudioRendererImpl::now_cb_ and clea..."

MSVC evaluates functions in a different order, causing test failures.

> Remove media::AudioRendererImpl::now_cb_ and clean up tests.
> 
> It's no longer needed as of r282376.
> 
> BUG=370634
> R=rileya@chromium.org
> 
> Review URL: https://codereview.chromium.org/380893002

TBR=scherkus@chromium.org

Review URL: https://codereview.chromium.org/380303004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282436 0039d316-1c4b-4281-b951-d872f2087c98

media/filters/audio_renderer_impl.cc

@@ -52,6 +52,7 @@ AudioRendererImpl::AudioRendererImpl(
                            decoders.Pass(),
                            set_decryptor_ready_cb),
       hardware_config_(hardware_config),
+      now_cb_(base::Bind(&base::TimeTicks::Now)),
       state_(kUninitialized),
       buffering_state_(BUFFERING_HAVE_NOTHING),
       rendering_(false),

media/filters/audio_renderer_impl.h

@@ -80,6 +80,12 @@ class MEDIA_EXPORT AudioRendererImpl
   virtual void StartPlayingFrom(base::TimeDelta timestamp) OVERRIDE;
   virtual void SetVolume(float volume) OVERRIDE;
 
+  // Allows injection of a custom time callback for non-realtime testing.
+  typedef base::Callback<base::TimeTicks()> NowCB;
+  void set_now_cb_for_testing(const NowCB& now_cb) {
+    now_cb_ = now_cb;
+  }
+
  private:
   friend class AudioRendererImplTest;
 
@@ -215,6 +221,9 @@ class MEDIA_EXPORT AudioRendererImpl
   // Callback provided to Flush().
   base::Closure flush_cb_;
 
+  // Typically calls base::TimeTicks::Now() but can be overridden by a test.
+  NowCB now_cb_;
+
   // After Initialize() has completed, all variables below must be accessed
   // under |lock_|. ------------------------------------------------------------
   base::Lock lock_;