[cc] Add SkBlendMode::kDstIn support to cc::Layer

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index e878a2020fb46732a3fd02938e91947f1fb818ab..f458f5d4bf137278c7b277cdea8101091b5c050f 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -501,10 +501,12 @@ void Layer::SetBlendMode(SkBlendMode blend_mode) {
   if (inputs_.blend_mode == blend_mode)
     return;
 
-  // Allowing only blend modes that are defined in the CSS Compositing standard:
+  // Allowing only blend modes that are defined in the CSS Compositing standard,
+  // plus destination-in which is used to implement masks.
   // http://dev.w3.org/fxtf/compositing-1/#blending
   switch (blend_mode) {
     case SkBlendMode::kSrcOver:
+    case SkBlendMode::kDstIn:
     case SkBlendMode::kScreen:
     case SkBlendMode::kOverlay:
     case SkBlendMode::kDarken:
@@ -527,7 +529,6 @@ void Layer::SetBlendMode(SkBlendMode blend_mode) {
     case SkBlendMode::kDst:
     case SkBlendMode::kDstOver:
     case SkBlendMode::kSrcIn:
-    case SkBlendMode::kDstIn:
     case SkBlendMode::kSrcOut:
     case SkBlendMode::kDstOut:
     case SkBlendMode::kSrcATop: