Update DirectWrite streams to SkStreamAsset.

SkTypefaces now deal in terms of SkStreamAsset, but the DirectWrite port
was never fully converted.

Review URL: https://codereview.chromium.org/940563002
diff --git a/src/utils/win/SkDWriteFontFileStream.h b/src/utils/win/SkDWriteFontFileStream.h
index f03518f..ba16f70 100644
--- a/src/utils/win/SkDWriteFontFileStream.h
+++ b/src/utils/win/SkDWriteFontFileStream.h
@@ -65,14 +65,15 @@
     virtual HRESULT STDMETHODCALLTYPE GetFileSize(UINT64* fileSize);
     virtual HRESULT STDMETHODCALLTYPE GetLastWriteTime(UINT64* lastWriteTime);
 
-    static HRESULT Create(SkStream* stream, SkDWriteFontFileStreamWrapper** streamFontFileStream);
+    static HRESULT Create(SkStreamAsset* stream,
+                          SkDWriteFontFileStreamWrapper** streamFontFileStream);
 
 private:
-    explicit SkDWriteFontFileStreamWrapper(SkStream* stream);
+    explicit SkDWriteFontFileStreamWrapper(SkStreamAsset* stream);
     virtual ~SkDWriteFontFileStreamWrapper() { }
 
     ULONG fRefCount;
-    SkAutoTDelete<SkStream> fStream;
+    SkAutoTDelete<SkStreamAsset> fStream;
     SkMutex fStreamMutex;
 };
 #endif