Move FPDF_FILEWRITE adapter to own file

This Cl moves the adapater out of the fpdfsave.cpp file into its own
h/cpp files. The adapter was renamed for clarity. The CPDF_Creator was
modified to take the adapter as a constructor param and the Create
methods consolidated.

Change-Id: Icb104f195ef532dda053c859aae356a8d4a7a54c
Reviewed-on: https://pdfium-review.googlesource.com/5151
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/fsdk_filewriteadapter.cpp b/fpdfsdk/fsdk_filewriteadapter.cpp
new file mode 100644
index 0000000..98ca3af
--- /dev/null
+++ b/fpdfsdk/fsdk_filewriteadapter.cpp
@@ -0,0 +1,18 @@
+// Copyright 2017 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
+
+#include "fpdfsdk/fsdk_filewriteadapter.h"
+
+FSDK_FileWriteAdapter::FSDK_FileWriteAdapter(FPDF_FILEWRITE* fileWriteStruct)
+    : fileWriteStruct_(fileWriteStruct) {
+  ASSERT(fileWriteStruct_);
+}
+
+FSDK_FileWriteAdapter::~FSDK_FileWriteAdapter() {}
+
+bool FSDK_FileWriteAdapter::WriteBlock(const void* data, size_t size) {
+  return fileWriteStruct_->WriteBlock(fileWriteStruct_, data, size) != 0;
+}