Implement setSinkId() for media elements without src.

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 623fd1679c52b25ea070f4fb974b3ecbe4f00856..c2519338ad7476d3bb9464c32467ec7db6894126 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -17,6 +17,7 @@
 #include "base/process/process.h"
 #include "base/strings/string16.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "cc/base/switches.h"
 #include "components/scheduler/renderer/renderer_scheduler.h"
@@ -78,6 +79,7 @@
 #include "content/renderer/ime_event_guard.h"
 #include "content/renderer/internal_document_state_data.h"
 #include "content/renderer/manifest/manifest_manager.h"
+#include "content/renderer/media/audio_device_factory.h"
 #include "content/renderer/media/audio_renderer_mixer_manager.h"
 #include "content/renderer/media/crypto/render_cdm_factory.h"
 #include "content/renderer/media/media_permission_dispatcher_impl.h"
@@ -111,6 +113,7 @@
 #include "content/renderer/web_ui_extension.h"
 #include "content/renderer/websharedworker_proxy.h"
 #include "gin/modules/module_registry.h"
+#include "media/audio/audio_output_device.h"
 #include "media/base/audio_renderer_mixer_input.h"
 #include "media/base/media_log.h"
 #include "media/blink/webencryptedmediaclient_impl.h"
@@ -5293,4 +5296,28 @@ mojo::ServiceProviderPtr RenderFrameImpl::ConnectToApplication(
   return service_provider.Pass();
 }
 
+void RenderFrameImpl::checkIfAudioSinkExistsAndIsAuthorized(
+    const blink::WebString& sink_id,
+    const blink::WebSecurityOrigin& security_origin,
+    blink::WebSetSinkIdCallbacks* web_callback) {
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE,
+      base::Bind(&RenderFrameImpl::DoCheckIfAudioSinkExistsAndIsAuthorized,

[Peter Beverloo, 2015/11/09 20:05:06]

There is a really subtle case in which this PostTask matters (even though the
implementation of the check is synchronous) - while resolving the promise will
use a microtask and thus appear asynchronous to the developer, not having this
PostTask would cause HTMLMediaElementAudioOutputDevice.m_sinkId to be
synchronously updated, which *can* be observed.

Firstly, I think it would be worth documenting this somewhere - perhaps add a
comment here briefly explaining why the PostTask to the same thread matters, it
may confuse a reader.

Secondly, this would be a good case to test in the layout test, which now
doesn't check the `sinkId` property at all.

  (1) Assert that element.sinkId == ''
  (2) Call element.setSinkId('somevalue')
  (3) Assert that element.sinkId == ''
  (4) Once the promise resolves, element.sinkId == 'somevalue'

(Are there keywords we can use for this kind of pass-through?)

[Guido Urdaneta, 2015/11/10 15:36:51]

I changed the implementation so that it is made asynchronous in Blink.
The reason is that when I added the mock version of
checkIfAudioSinkExistsAndIsAuthorized() to WebFrameTestProxy, the promise was
resolved/rejected too quickly and the layout test was getting undefined as the
result of setSinkId() instead of a Promise object. I don't know if this is a
feature or a bug, but it did not happen in tests when the real implementation
was used.
The sinkId property check was added to the test.

+                 weak_factory_.GetWeakPtr(), sink_id.utf8(),
+                 static_cast<url::Origin>(security_origin),
+                 media::ConvertToSwitchOutputDeviceCB(web_callback)));
+}
+
+void RenderFrameImpl::DoCheckIfAudioSinkExistsAndIsAuthorized(
+    const std::string& device_id,
+    const url::Origin& security_origin,
+    const media::SwitchOutputDeviceCB& callback) {
+  scoped_refptr<media::AudioOutputDevice> device =
+      AudioDeviceFactory::NewOutputDevice(routing_id_, 0, device_id,
+                                          security_origin);
+  media::OutputDeviceStatus status = device->GetDeviceStatus();
+  device->Stop();
+  callback.Run(status);
+}
+
 }  // namespace content