Move metafile printing code from platform canvas to PaintCanvas

cc/paint/paint_canvas.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_PAINT_PAINT_CANVAS_H_
 #define CC_PAINT_PAINT_CANVAS_H_
 
 #include "cc/paint/paint_export.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/utils/SkNWayCanvas.h"
 #include "third_party/skia/include/utils/SkNoDrawCanvas.h"
 
 namespace cc {
 
 using PaintCanvas = SkCanvas;
 using PaintCanvasNoDraw = SkNoDrawCanvas;
 using PaintCanvasAutoRestore = SkAutoCanvasRestore;
 
 class CC_PAINT_EXPORT PaintCanvasPassThrough : public SkNWayCanvas {
  public:
   explicit PaintCanvasPassThrough(SkCanvas* canvas);
   PaintCanvasPassThrough(int width, int height);
   ~PaintCanvasPassThrough() override;
 };
 
+// TODO(enne): Move all these functions into PaintCanvas.
+
 // PaintCanvas equivalent of skia::GetWritablePixels.
 CC_PAINT_EXPORT bool ToPixmap(PaintCanvas* canvas, SkPixmap* output);
 
+// Following routines are used in print preview workflow to mark the
+// preview metafile.
+#if defined(OS_MACOSX)
+CC_PAINT_EXPORT void SetIsPreviewMetafile(PaintCanvas* canvas, bool is_preview);
+CC_PAINT_EXPORT bool IsPreviewMetafile(PaintCanvas* canvas);
+#endif
+
 }  // namespace cc
 
 #endif  // CC_PAINT_PAINT_CANVAS_H_