Implement setSinkId() for media elements without src.

third_party/WebKit/public/web/WebFrameClient.h

Index: third_party/WebKit/public/web/WebFrameClient.h
diff --git a/third_party/WebKit/public/web/WebFrameClient.h b/third_party/WebKit/public/web/WebFrameClient.h
index fd520576316b589f50d9d4fd4d2f0737b0088d9d..91fd6827227792e81ff0a57ad0616c1383e033f1 100644
--- a/third_party/WebKit/public/web/WebFrameClient.h
+++ b/third_party/WebKit/public/web/WebFrameClient.h
@@ -48,6 +48,7 @@
 #include "public/platform/WebFileSystem.h"
 #include "public/platform/WebFileSystemType.h"
 #include "public/platform/WebSecurityOrigin.h"
+#include "public/platform/WebSetSinkIdCallbacks.h"
 #include "public/platform/WebStorageQuotaCallbacks.h"
 #include "public/platform/WebStorageQuotaType.h"
 #include "public/platform/WebURLError.h"
@@ -674,6 +675,12 @@ public:
     // WebUSB --------------------------------------------------------------
     virtual WebUSBClient* usbClient() { return nullptr; }
 
+
+    // Audio Output Devices API --------------------------------------------
+
+    // Checks that the given audio sink exists and is authorized. The result is provided via the callback.
+    virtual void checkAudioSink(const WebString& sinkId, const WebSecurityOrigin&, WebSetSinkIdCallbacks*) { }

[jochen (gone - plz use gerrit), 2015/10/28 14:18:49]

why does this not just return the result? It seems like the callback is executed
synchronously anyway?

can we call the method something like checkIfAudioSinkExistsAndIsAuthorized?

[Guido Urdaneta, 2015/10/28 15:58:44]

It's simpler to leave the callback for two reasons:
1. This is used only in a context where the callback is available, as that is
the existing mechanism to communicate the results to the upper layer.
2. Error results are in an enum that contains only error codes with no value for
success. Thus, we would need to return two values: a bool to indicate
success/failure, and an enum to indicate the error code in case of failures. I
think this would look less clean than the callback.
3. We would need extra logic in RenderFrameImpl to translate the chromium status
code to the bool/enum combination, and also extra logic in Blink to decide
whether to call onSuccess() or onError() to communicate the result upstream.
Using the callback allows us to use the already existing logic in Chromium to do
all this with just a couple of statements.

If you think these reasons are not good enough I can of course change it.
Done.

[jochen (gone - plz use gerrit), 2015/10/28 16:06:47]

 ok, then at least postTask the callback so nobody accidentally can rely on it
being sync

[Guido Urdaneta, 2015/10/28 17:20:10]

Done. I PostTasked the whole logic, except for type conversions.

+
 protected:
     virtual ~WebFrameClient() { }
 };