Split the existing PDFFunction in two classes, a private PDFFunction and a public PDFFunctionFactory, and utilize the latter in PDFDocument to allow various code to access the methods of PDFFunction`

*Follow-up to PR 8909.*

This requires us to pass around `pdfFunctionFactory` to quite a lot of existing code, however I don't see another way of handling this while still guaranteeing that we can access `PDFFunction` as freely as in the old code.

Please note that the patch passes all tests locally (unit, font, reference), and I *very* much hope that we have sufficient test-coverage for the code in question to catch any typos/mistakes in the re-factoring.

src/core/pattern.js

@@ -20,7 +20,6 @@ import {
 } from '../shared/util';
 import { ColorSpace } from './colorspace';
 import { isStream } from './primitives';
-import { PDFFunction } from './function';
 
 var ShadingType = {
   FUNCTION_BASED: 1,
@@ -46,9 +45,8 @@ var Pattern = (function PatternClosure() {
     },
   };
 
-  Pattern.parseShading = function Pattern_parseShading(shading, matrix, xref,
-                                                       res, handler) {
-
+  Pattern.parseShading = function(shading, matrix, xref, res, handler,
+                                  pdfFunctionFactory) {
     var dict = isStream(shading) ? shading.dict : shading;
     var type = dict.get('ShadingType');
 
@@ -57,12 +55,14 @@ var Pattern = (function PatternClosure() {
         case ShadingType.AXIAL:
         case ShadingType.RADIAL:
           // Both radial and axial shadings are handled by RadialAxial shading.
-          return new Shadings.RadialAxial(dict, matrix, xref, res);
+          return new Shadings.RadialAxial(dict, matrix, xref, res,
+                                          pdfFunctionFactory);
         case ShadingType.FREE_FORM_MESH:
         case ShadingType.LATTICE_FORM_MESH:
         case ShadingType.COONS_PATCH_MESH:
         case ShadingType.TENSOR_PATCH_MESH:
-          return new Shadings.Mesh(shading, matrix, xref, res);
+          return new Shadings.Mesh(shading, matrix, xref, res,
+                                   pdfFunctionFactory);
         default:
           throw new FormatError('Unsupported ShadingType: ' + type);
       }
@@ -88,13 +88,13 @@ Shadings.SMALL_NUMBER = 1e-6;
 // Radial and axial shading have very similar implementations
 // If needed, the implementations can be broken into two classes
 Shadings.RadialAxial = (function RadialAxialClosure() {
-  function RadialAxial(dict, matrix, xref, res) {
+  function RadialAxial(dict, matrix, xref, res, pdfFunctionFactory) {
     this.matrix = matrix;
     this.coordsArr = dict.getArray('Coords');
     this.shadingType = dict.get('ShadingType');
     this.type = 'Pattern';
     var cs = dict.get('ColorSpace', 'CS');
-    cs = ColorSpace.parse(cs, xref, res);
+    cs = ColorSpace.parse(cs, xref, res, pdfFunctionFactory);
     this.cs = cs;
 
     var t0 = 0.0, t1 = 1.0;
@@ -132,7 +132,7 @@ Shadings.RadialAxial = (function RadialAxialClosure() {
     this.extendEnd = extendEnd;
 
     var fnObj = dict.get('Function');
-    var fn = PDFFunction.parseArray(xref, fnObj);
+    var fn = pdfFunctionFactory.createFromArray(fnObj);
 
     // 10 samples seems good enough for now, but probably won't work
     // if there are sharp color changes. Ideally, we would implement
@@ -711,7 +711,7 @@ Shadings.Mesh = (function MeshClosure() {
     }
   }
 
-  function Mesh(stream, matrix, xref, res) {
+  function Mesh(stream, matrix, xref, res, pdfFunctionFactory) {
     if (!isStream(stream)) {
       throw new FormatError('Mesh data is not a stream');
     }
@@ -721,13 +721,13 @@ Shadings.Mesh = (function MeshClosure() {
     this.type = 'Pattern';
     this.bbox = dict.getArray('BBox');
     var cs = dict.get('ColorSpace', 'CS');
-    cs = ColorSpace.parse(cs, xref, res);
+    cs = ColorSpace.parse(cs, xref, res, pdfFunctionFactory);
     this.cs = cs;
     this.background = dict.has('Background') ?
       cs.getRgb(dict.get('Background'), 0) : null;
 
     var fnObj = dict.get('Function');
-    var fn = fnObj ? PDFFunction.parseArray(xref, fnObj) : null;
+    var fn = fnObj ? pdfFunctionFactory.createFromArray(fnObj) : null;
 
     this.coords = [];
     this.colors = [];