add missing API

include/core/SkStream.h

Index: include/core/SkStream.h
diff --git a/include/core/SkStream.h b/include/core/SkStream.h
index e311a4ac4991d8b511b8b43f2a39ff8079ac05ec..a6a62c42ba1b7dd9c08264eed0417a40fa0d8264 100644
--- a/include/core/SkStream.h
+++ b/include/core/SkStream.h
@@ -370,7 +370,7 @@ private:
     typedef SkWStream INHERITED;
 };
 
-class SkMemoryWStream : public SkWStream {
+class SK_API SkMemoryWStream : public SkWStream {
 public:
     SkMemoryWStream(void* buffer, size_t size);
     bool write(const void* buffer, size_t size) override;