cc : Delete layer's draw blend mode

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 27785c86ad35377dc1a6792a5fd77d3ceaf0f7f5..523b01f830f4a52408dbfb401a4f82ccbdaa4197 100644
--- a/cc/trees/occlusion_tracker.cc
+++ b/cc/trees/occlusion_tracker.cc
@@ -335,10 +335,6 @@ void OcclusionTracker::MarkOccludedBehindLayer(const LayerImpl* layer) {
   if (layer->draw_opacity() < 1)
     return;
 
-  // The only currently supported draw_blend_mode is SrcOver mode, so
-  // draw_blend_mode does not affect occlusion.
-  DCHECK_EQ(layer->draw_blend_mode(), SkBlendMode::kSrcOver);
-
   if (layer->Is3dSorted())
     return;