stop using SkXfermode -- use SkBlendMode instead

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 85b517e7147eb6177d29f29e0341535425006d45..ed737dcc9cf3acedc66b6998e90443640144d2f2 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -731,7 +731,7 @@ static void AppendQuadsToFillScreen(const gfx::Rect& root_scroll_layer_rect,
       target_render_pass->CreateAndAppendSharedQuadState();
   shared_quad_state->SetAll(gfx::Transform(), root_target_rect.size(),
                             root_target_rect, root_target_rect, false, opacity,
-                            SkXfermode::kSrcOver_Mode, sorting_context_id);
+                            SkBlendMode::kSrcOver, sorting_context_id);
 
   for (Region::Iterator fill_rects(fill_region); fill_rects.has_rect();
        fill_rects.next()) {