Mac Overlays: Add sandwich strategy

content/browser/compositor/browser_compositor_overlay_candidate_validator_ozone.cc

Index: content/browser/compositor/browser_compositor_overlay_candidate_validator_ozone.cc
diff --git a/content/browser/compositor/browser_compositor_overlay_candidate_validator_ozone.cc b/content/browser/compositor/browser_compositor_overlay_candidate_validator_ozone.cc
index b55c71647e4d8104cbb8b614fcfffd1ea322d725..05ba4a3d4af54ec8ddc89f3c04adf862e06a6e3e 100644
--- a/content/browser/compositor/browser_compositor_overlay_candidate_validator_ozone.cc
+++ b/content/browser/compositor/browser_compositor_overlay_candidate_validator_ozone.cc
@@ -4,6 +4,8 @@
 
 #include "content/browser/compositor/browser_compositor_overlay_candidate_validator_ozone.h"
 
+#include "cc/output/overlay_strategy_single_on_top.h"
+#include "cc/output/overlay_strategy_underlay.h"
 #include "ui/ozone/public/overlay_candidates_ozone.h"
 
 namespace content {
@@ -33,6 +35,14 @@ BrowserCompositorOverlayCandidateValidatorOzone::
     ~BrowserCompositorOverlayCandidateValidatorOzone() {
 }
 
+void BrowserCompositorOverlayCandidateValidatorOzone::GetStrategies(
+    cc::OverlayProcessor::StrategyList* strategies) {
+  strategies->push_back(scoped_ptr<cc::OverlayProcessor::Strategy>(
+      new cc::OverlayStrategyCommon(this, new cc::OverlayStrategySingleOnTop)));
+  strategies->push_back(scoped_ptr<cc::OverlayProcessor::Strategy>(
+      new cc::OverlayStrategyCommon(this, new cc::OverlayStrategyUnderlay)));
+}
+
 void BrowserCompositorOverlayCandidateValidatorOzone::CheckOverlaySupport(
     cc::OverlayCandidateList* surfaces) {
   // SW mirroring copies out of the framebuffer, so we can't remove any