Presentation API: allow the Mojo service to reject a getAvailability() call.

content/renderer/presentation/presentation_dispatcher.cc

Index: content/renderer/presentation/presentation_dispatcher.cc
diff --git a/content/renderer/presentation/presentation_dispatcher.cc b/content/renderer/presentation/presentation_dispatcher.cc
index c1cf36ea8cd2df4ca77c15dc42a9bf21aa086ca4..6c68708facb2d4b85d98e37d647ac582eec2f465 100644
--- a/content/renderer/presentation/presentation_dispatcher.cc
+++ b/content/renderer/presentation/presentation_dispatcher.cc
@@ -355,6 +355,23 @@ void PresentationDispatcher::OnScreenAvailabilityUpdated(bool available) {
   UpdateListeningState();
 }
 
+void PresentationDispatcher::OnScreenAvailabilityNotSupported() {
+  DCHECK(listening_state_ == ListeningState::Waiting);
+
+  for (AvailabilityCallbacksMap::iterator iter(&availability_callbacks_);
+       !iter.IsAtEnd(); iter.Advance()) {
+    iter.GetCurrentValue()->onError(new blink::WebPresentationError(
+        blink::WebPresentationError::ErrorTypeAvailabilityNotSupported,
+        blink::WebString::fromUTF8(
+            "getAvailability() isn't supported at the moment. It can be due to"
+            "a permanent or temporary system limitation. It is recommended to"
+            "try to blindly start a session in that case.")));
+  }
+  availability_callbacks_.Clear();
+
+  UpdateListeningState();
+}
+
 void PresentationDispatcher::OnDefaultSessionStarted(
     presentation::PresentationSessionInfoPtr session_info) {
   if (!controller_)