Add temporary header to shift clients over to include/core/SkDeferredDisplayList.h

The plan is:
Add SkDDLTmpRedirect.h
update clients to point to SkDDLTmpRedirect.h
Move SkDeferredDisplayList.h to include/core (and update SkDDLTmpRedirect.h)
update clients to point to SkDeferredDisplayList.h in its new location
remove SkDDLTmpRedirect.h

This staging is required to land:

https://skia-review.googlesource.com/c/skia/+/272343 (Move SkDeferredDisplayList.h into include\core)

Change-Id: I3302cdb8607b259d084bb9dd00600652c7f9a93a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272460
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/gn/core.gni b/gn/core.gni
index 7d59209..d4817ae 100644
--- a/gn/core.gni
+++ b/gn/core.gni
@@ -459,6 +459,7 @@
   # private
   "$_include/private/SkChecksum.h",
   "$_include/private/SkColorData.h",
+  "$_include/private/SkDDLTmpRedirect.h",
   "$_include/private/SkDeferredDisplayList.h",
   "$_include/private/SkDeque.h",
   "$_include/private/SkFixed.h",
diff --git a/include/private/SkDDLTmpRedirect.h b/include/private/SkDDLTmpRedirect.h
new file mode 100644
index 0000000..71684f3
--- /dev/null
+++ b/include/private/SkDDLTmpRedirect.h
@@ -0,0 +1,15 @@
+/*
+ * Copyright 2020 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkDDLTmpRedirect_DEFINED
+#define SkDDLTmpRedirect_DEFINED
+
+// A client is directly referencing include/private/SkDeferredDisplayList.h. This temporary
+// header is required to move them over to referencing include/core/SkDeferredDisplayList.h.
+#include "include/private/SkDeferredDisplayList.h"
+
+#endif