add fsync to try to get complete skps from webpage picture capture

include/core/SkStream.h

Index: include/core/SkStream.h
diff --git a/include/core/SkStream.h b/include/core/SkStream.h
index 44de6e87e11427ef567127bd6adc47616732bba5..f4c1b0db32c3e10a893b12455f453fc7f0120b8c 100644
--- a/include/core/SkStream.h
+++ b/include/core/SkStream.h
@@ -192,6 +192,7 @@ public:
     virtual bool write(const void* buffer, size_t size) = 0;
     virtual void newline();
     virtual void flush();
+    virtual void sync();
 
     virtual size_t bytesWritten() const = 0;
 
@@ -360,6 +361,7 @@ public:
 
     bool write(const void* buffer, size_t size) override;
     void flush() override;
+    void sync() override;
     size_t bytesWritten() const override;
 
 private: