begin to hide details of SkPathEffect

BUG=skia:

Change-Id: I155d2370ae894e6000b6a768d02cf06bf5b3de6e
Reviewed-on: https://skia-review.googlesource.com/8977
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/public.bzl b/public.bzl
index f4b9ef9..2fa7a54 100644
--- a/public.bzl
+++ b/public.bzl
@@ -599,6 +599,7 @@
     "SK_NO_ANALYTIC_AA",
     "SK_SUPPORT_LEGACY_BITMAP_SETPIXELREF",
     "SK_SUPPORT_LEGACY_CLIPOP_EXOTIC_NAMES",
+    "SK_SUPPORT_LEGACY_PATHEFFECT_SUBCLASSES",
 ]
 
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