Reland "add a stub for running fiddles as GMs"

This is a reland of adfc22df860a9175713d50a507bf5dbb3ee32415

PS2+3 restrict this to just local builds: no G3, no Android, etc.

Original change's description:
> add a stub for running fiddles as GMs
>
> This is about the 15th time I've hacked this up.
>
> Change-Id: I0c75c0d04133d867e942c39eba693fd7227ba0f5
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/233240
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Mike Klein <mtklein@google.com>

Change-Id: I7b8e7418edc4949c2f3e07ddf01f0643344397d1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/233242
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/gm/fiddle.cpp b/gm/fiddle.cpp
new file mode 100644
index 0000000..dd57f2f
--- /dev/null
+++ b/gm/fiddle.cpp
@@ -0,0 +1,15 @@
+/*
+ * Copyright 2019 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm/gm.h"
+#include "skia.h"
+
+static void draw(SkCanvas* canvas);
+DEF_SIMPLE_GM(fiddle, canvas, 256, 256) { draw(canvas); }
+
+// Paste your fiddle.skia.org code over this stub.
+void draw(SkCanvas*) {}