Output blend mode when dumping cc::EffectNode

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Iba7a5721a587ad1713e1e7e5f7eae0611af389d3
Reviewed-on: https://chromium-review.googlesource.com/1239203Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593356}

cc/trees/effect_node.cc

@@ -80,6 +80,7 @@ void EffectNode::AsValueInto(base::trace_event::TracedValue* value) const {
   value->SetInteger("parent_id", parent_id);
   value->SetInteger("stable_id", stable_id);
   value->SetDouble("opacity", opacity);
+  value->SetString("blend_mode", SkBlendMode_Name(blend_mode));
   value->SetBoolean("has_render_surface", has_render_surface);
   value->SetBoolean("cache_render_surface", cache_render_surface);
   value->SetBoolean("has_copy_request", has_copy_request);