ozone: Add overlay candidate implementation that queries support via IPC

ui/ozone/common/stub_overlay_manager.cc

Index: ui/ozone/common/stub_overlay_manager.cc
diff --git a/ui/ozone/common/stub_overlay_manager.cc b/ui/ozone/common/stub_overlay_manager.cc
index d39d4bf8c22170b314cd5d0403abfda04637ddd8..790d8a62431a18242056947452728ce07cb696d8 100644
--- a/ui/ozone/common/stub_overlay_manager.cc
+++ b/ui/ozone/common/stub_overlay_manager.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "ui/ozone/common/stub_overlay_manager.h"
+#include "ui/ozone/public/overlay_candidates_ozone.h"
 
 namespace ui {
 
@@ -12,7 +13,7 @@ StubOverlayManager::StubOverlayManager() {
 StubOverlayManager::~StubOverlayManager() {
 }
 
-OverlayCandidatesOzone* StubOverlayManager::GetOverlayCandidates(
+scoped_ptr<OverlayCandidatesOzone> StubOverlayManager::GetOverlayCandidates(
     gfx::AcceleratedWidget w) {
   return nullptr;
 }