cc: RenderSurfaceImpl tile mask layer.

cc/layers/picture_layer.cc

Index: cc/layers/picture_layer.cc
diff --git a/cc/layers/picture_layer.cc b/cc/layers/picture_layer.cc
index 6cacd6fca499d11388277351b805970c77e541e6..7c1502085e997d7e2c41486ce17238913a51770c 100644
--- a/cc/layers/picture_layer.cc
+++ b/cc/layers/picture_layer.cc
@@ -146,6 +146,11 @@ bool PictureLayer::Update() {
 }
 
 void PictureLayer::SetLayerMaskType(LayerMaskType mask_type) {
+  // We do not allow converting SINGLE_TEXTURE_MASK to MULTI_TEXTURE_MASK in
+  // order to avoid rerastering when a mask's transform is being animated.
+  if (mask_type_ == LayerMaskType::SINGLE_TEXTURE_MASK &&
+      LayerMaskType::MULTI_TEXTURE_MASK)
+    return;
   mask_type_ = mask_type;
 }