mix-blend-mode implementation for accelerated layers

cc/trees/occlusion_tracker.cc

Index: cc/trees/occlusion_tracker.cc
diff --git a/cc/trees/occlusion_tracker.cc b/cc/trees/occlusion_tracker.cc
index 7e24e840cee122739147418d46d1f5507dc61191..79a40c38111456a6cd84d3c997a36313d0998c0a 100644
--- a/cc/trees/occlusion_tracker.cc
+++ b/cc/trees/occlusion_tracker.cc
@@ -236,6 +236,7 @@ void OcclusionTrackerBase<LayerType, RenderSurfaceType>::FinishedRenderTarget(
   if (finished_target->mask_layer() ||
       !SurfaceOpacityKnown(surface) ||
       surface->draw_opacity() < 1 ||
+      !finished_target->uses_default_blend_mode() ||
       target_is_only_for_copy_request ||
       finished_target->filters().HasFilterThatAffectsOpacity()) {
     stack_.back().occlusion_from_outside_target.Clear();
@@ -417,6 +418,9 @@ void OcclusionTrackerBase<LayerType, RenderSurfaceType>::
   if (!LayerOpacityKnown(layer) || layer->draw_opacity() < 1)
     return;
 
+  if (!layer->uses_default_blend_mode())
+    return;
+
   if (LayerIsInUnsorted3dRenderingContext(layer))
     return;