Implement setSinkId() for media elements without src.

components/test_runner/web_frame_test_proxy.h

Index: components/test_runner/web_frame_test_proxy.h
diff --git a/components/test_runner/web_frame_test_proxy.h b/components/test_runner/web_frame_test_proxy.h
index 00a287c4b2a496e212455756b22970c0c3b79235..31ec31c73b3ab25fa4d992ddf5498aa01c851035 100644
--- a/components/test_runner/web_frame_test_proxy.h
+++ b/components/test_runner/web_frame_test_proxy.h
@@ -274,6 +274,14 @@ class WebFrameTestProxy : public Base {
     Base::postAccessibilityEvent(object, event);
   }
 
+  virtual void checkIfAudioSinkExistsAndIsAuthorized(
+      const blink::WebString& sink_id,
+      const blink::WebSecurityOrigin& security_origin,
+      blink::WebSetSinkIdCallbacks* web_callbacks) {
+    base_proxy_->CheckIfAudioSinkExistsAndIsAuthorized(sink_id, security_origin,
+                                                       web_callbacks);
+  }
+
  private:
   WebTestProxyBase* base_proxy_;