Trace 'should flatten' and layer transform

BUG=None
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1849543002

Cr-Commit-Position: refs/heads/master@{#384071}
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index bcbec39..cdc340d 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -1409,6 +1409,11 @@
 
   MathUtil::AddToTracedValue("transform_origin", transform_origin_, state);
 
+  if (!transform().IsIdentity())
+    MathUtil::AddToTracedValue("transform", transform(), state);
+
+  state->SetBoolean("should_flatten", should_flatten_transform_);
+
   bool clipped;
   gfx::QuadF layer_quad =
       MathUtil::MapQuad(ScreenSpaceTransform(),