add missing API

include/core/SkStream.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkStream_DEFINED
 #define SkStream_DEFINED
 
@@ skipping 352 matching lines @@
     void flush() override;
     void fsync();
     size_t bytesWritten() const override;
 
 private:
     FILE* fFILE;
 
     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;
     size_t bytesWritten() const override { return fBytesWritten; }
 
 private:
     char*   fBuffer;
     size_t  fMaxLength;
     size_t  fBytesWritten;
 
@@ skipping 57 matching lines @@
 
 private:
     size_t fBytesWritten;
     typedef SkWStream INHERITED;
 };
 
 // for now
 typedef SkFILEStream SkURLStream;
 
 #endif