Move metafile printing code from platform canvas to PaintCanvas

cc/paint/paint_canvas.h

Index: cc/paint/paint_canvas.h
diff --git a/cc/paint/paint_canvas.h b/cc/paint/paint_canvas.h
index 6df34439c315f69544fe83ae0d27c7be7815e456..7767240d53e9466158a2a258255f2c162ea51dd2 100644
--- a/cc/paint/paint_canvas.h
+++ b/cc/paint/paint_canvas.h
@@ -23,9 +23,18 @@ class CC_PAINT_EXPORT PaintCanvasPassThrough : public SkNWayCanvas {
   ~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_