[skottie] SK_API-export public classes

TBR=
Change-Id: I14fcbf0932ff5c6de6fc4b500647f74d55d72266
Reviewed-on: https://skia-review.googlesource.com/129463
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/experimental/skottie/Skottie.h b/experimental/skottie/Skottie.h
index 275127a..0a89ca0 100644
--- a/experimental/skottie/Skottie.h
+++ b/experimental/skottie/Skottie.h
@@ -25,14 +25,14 @@
 
 namespace json { class ValueRef; }
 
-class ResourceProvider : public SkNoncopyable {
+class SK_API ResourceProvider : public SkNoncopyable {
 public:
     virtual ~ResourceProvider() = default;
 
     virtual std::unique_ptr<SkStream> openStream(const char resource[]) const = 0;
 };
 
-class Animation : public SkRefCnt {
+class SK_API Animation : public SkRefCnt {
 public:
     struct Stats {
         float  fTotalLoadTimeMS,