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 e52f9c93329793135dd02f9c1e8425e7082b18c9..4e6a3c7281915178832a93451171719b7b46ed64 100644
--- a/content/renderer/presentation/presentation_dispatcher.cc
+++ b/content/renderer/presentation/presentation_dispatcher.cc
@@ -348,6 +348,9 @@ void PresentationDispatcher::OnScreenAvailabilityUpdated(bool available) {
   for (auto observer : availability_observers_)
     observer->availabilityChanged(available);
 
+  for (auto observer : availability_observers_)
+    observer->availabilityChanged(available);
+
   for (AvailabilityCallbacksMap::iterator iter(&availability_callbacks_);
        !iter.IsAtEnd(); iter.Advance()) {
     iter.GetCurrentValue()->onSuccess(new bool(available));
@@ -357,6 +360,23 @@ 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_)