Allow AudioDevice to be constructed on any thread

content/renderer/media/audio_device.cc

Index: content/renderer/media/audio_device.cc
===================================================================
--- content/renderer/media/audio_device.cc	(revision 142824)
+++ content/renderer/media/audio_device.cc	(working copy)
@@ -46,7 +46,7 @@
       stream_id_(0),
       play_on_start_(true),
       is_started_(false) {
-  filter_ = RenderThreadImpl::current()->audio_message_filter();
+  filter_ = AudioMessageFilter::current();

[henrika (OOO until Aug 14), 2012/06/20 12:33:52]

By not injecting you make it much more difficult to mock the AudioDevice;
something that we will need given how many clients that are using it.  Try
adding a simple unit test where all you do is to create and destroy and
AudioDevice and you will see what I mean.

[henrika (OOO until Aug 14), 2012/06/20 17:15:53]

Bad example; sorry. I meant create the AD and perform any operation on it which
requires an existing filter.

 }
 
 AudioDevice::AudioDevice(const media::AudioParameters& params,
@@ -58,7 +58,7 @@
       stream_id_(0),
       play_on_start_(true),
       is_started_(false) {
-  filter_ = RenderThreadImpl::current()->audio_message_filter();
+  filter_ = AudioMessageFilter::current();
 }
 
 void AudioDevice::Initialize(const media::AudioParameters& params,