SkDeflateWStream: support gzip output

src/pdf/SkDeflate.h

-
 /*
  * Copyright 2010 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 SkFlate_DEFINED
 #define SkFlate_DEFINED
 
 #include "SkTypes.h"
 
 #include "SkStream.h"
 
 /**
   * Wrap a stream in this class to compress the information written to
-  * this stream using the Deflate algorithm.  Uses Zlib's
-  * Z_DEFAULT_COMPRESSION level.
+  * this stream using the Deflate algorithm.
   *
   * See http://en.wikipedia.org/wiki/DEFLATE
   */
 class SkDeflateWStream final : public SkWStream {
 public:
-    /** Does not take ownership of the stream. */
-    SkDeflateWStream(SkWStream*);
+    /** Does not take ownership of the stream.
+
+        @param compressionLevel - 0 is no compression; 1 is best
+        speed; 9 is best compression.  The default, -1, is to use
+        zlib's Z_DEFAULT_COMPRESSION level.
+
+        @param gzip iff true, output a gzip file. "The gzip format is
+        a wrapper, documented in RFC 1952, around a deflate stream."
+        gzip adds a header with a magic number to the beginning of the
+        stream, alowing a client to identify a gzip file.
+     */
+    SkDeflateWStream(SkWStream*,
+                     int compressionLevel = -1,
+                     bool gzip = false);
 
     /** The destructor calls finalize(). */
     ~SkDeflateWStream();
 
     /** Write the end of the compressed stream.  All subsequent calls to
         write() will fail. Subsequent calls to finalize() do nothing. */
     void finalize();
 
     // The SkWStream interface:
     bool write(const void*, size_t) override;
     size_t bytesWritten() const override;
 
 private:
     struct Impl;
     SkAutoTDelete<Impl> fImpl;
 };
 
 #endif  // SkFlate_DEFINED