Reland "hide drawlooper from paint"

This reverts commit 6dc14ded91ea72c9b7bb8c89453c377be3236c89.

Reason for revert: add flag to google3

Original change's description:
> Revert "hide drawlooper from paint"
>
> This reverts commit 766b42b7ba8e421cf1a3bccdcb523e37ac1a40ab.
>
> Reason for revert: afaict this is changing a lot of image filter GMs for the worse
>
> Original change's description:
> > hide drawlooper from paint
> >
> > Bug: skia: 4783
> >
> > Change-Id: I1d0ad1683a2e8345d8ea13db9b69b568ada827dc
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/228573
> > Reviewed-by: Florin Malita <fmalita@chromium.org>
> > Commit-Queue: Mike Reed <reed@google.com>
>
> TBR=fmalita@chromium.org,reed@google.com
>
> Change-Id: I0bfd48ada3f8e48a774527caccf7abdb7a1cc470
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: skia: 4783
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/229005
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>

TBR=robertphillips@google.com,fmalita@chromium.org,reed@google.com

Change-Id: Ib3cd8941a63cd323b8872dd7fec1c953ab81cbdc
Bug: skia: 4783
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/229010
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/samplecode/SampleUnpremul.cpp b/samplecode/SampleUnpremul.cpp
index ec58491..3833068 100644
--- a/samplecode/SampleUnpremul.cpp
+++ b/samplecode/SampleUnpremul.cpp
@@ -20,6 +20,8 @@
 #include "tools/Resources.h"
 #include "tools/ToolUtils.h"
 
+#ifdef SK_SUPPORT_LEGACY_DRAWLOOPER
+
 /**
  *  Interprets c as an unpremultiplied color, and returns the
  *  premultiplied equivalent.
@@ -169,3 +171,5 @@
 //////////////////////////////////////////////////////////////////////////////
 
 DEF_SAMPLE( return new UnpremulView(GetResourcePath("images")); )
+
+#endif