Move worker-thread only functions from src/shared/util.js and into a new src/core/core_utils.js file

The `src/shared/util.js` file is being bundled into both the `pdf.js` and `pdf.worker.js` files, meaning that its code is by definition duplicated.
Some main-thread only utility functions have already been moved to a separate `src/display/display_utils.js` file, and this patch simply extends that concept to utility functions which are used *only* on the worker-thread.

Note in particular the `getInheritableProperty` function, which expects a `Dict` as input and thus *cannot* possibly ever be used on the main-thread.

src/core/core_utils.js

@@ -0,0 +1,160 @@
+/* Copyright 2019 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/* eslint no-var: error */
+
+import { assert, warn } from '../shared/util';
+
+function getLookupTableFactory(initializer) {
+  let lookup;
+  return function() {
+    if (initializer) {
+      lookup = Object.create(null);
+      initializer(lookup);
+      initializer = null;
+    }
+    return lookup;
+  };
+}
+
+const MissingDataException = (function MissingDataExceptionClosure() {
+  function MissingDataException(begin, end) {
+    this.begin = begin;
+    this.end = end;
+    this.message = `Missing data [${begin}, ${end})`;
+  }
+
+  MissingDataException.prototype = new Error();
+  MissingDataException.prototype.name = 'MissingDataException';
+  MissingDataException.constructor = MissingDataException;
+
+  return MissingDataException;
+})();
+
+const XRefEntryException = (function XRefEntryExceptionClosure() {
+  function XRefEntryException(msg) {
+    this.message = msg;
+  }
+
+  XRefEntryException.prototype = new Error();
+  XRefEntryException.prototype.name = 'XRefEntryException';
+  XRefEntryException.constructor = XRefEntryException;
+
+  return XRefEntryException;
+})();
+
+const XRefParseException = (function XRefParseExceptionClosure() {
+  function XRefParseException(msg) {
+    this.message = msg;
+  }
+
+  XRefParseException.prototype = new Error();
+  XRefParseException.prototype.name = 'XRefParseException';
+  XRefParseException.constructor = XRefParseException;
+
+  return XRefParseException;
+})();
+
+/**
+ * Get the value of an inheritable property.
+ *
+ * If the PDF specification explicitly lists a property in a dictionary as
+ * inheritable, then the value of the property may be present in the dictionary
+ * itself or in one or more parents of the dictionary.
+ *
+ * If the key is not found in the tree, `undefined` is returned. Otherwise,
+ * the value for the key is returned or, if `stopWhenFound` is `false`, a list
+ * of values is returned. To avoid infinite loops, the traversal is stopped when
+ * the loop limit is reached.
+ *
+ * @param {Dict} dict - Dictionary from where to start the traversal.
+ * @param {string} key - The key of the property to find the value for.
+ * @param {boolean} getArray - Whether or not the value should be fetched as an
+ *   array. The default value is `false`.
+ * @param {boolean} stopWhenFound - Whether or not to stop the traversal when
+ *   the key is found. If set to `false`, we always walk up the entire parent
+ *   chain, for example to be able to find `\Resources` placed on multiple
+ *   levels of the tree. The default value is `true`.
+ */
+function getInheritableProperty({ dict, key, getArray = false,
+                                  stopWhenFound = true, }) {
+  const LOOP_LIMIT = 100;
+  let loopCount = 0;
+  let values;
+
+  while (dict) {
+    const value = getArray ? dict.getArray(key) : dict.get(key);
+    if (value !== undefined) {
+      if (stopWhenFound) {
+        return value;
+      }
+      if (!values) {
+        values = [];
+      }
+      values.push(value);
+    }
+    if (++loopCount > LOOP_LIMIT) {
+      warn(`getInheritableProperty: maximum loop count exceeded for "${key}"`);
+      break;
+    }
+    dict = dict.get('Parent');
+  }
+  return values;
+}
+
+const ROMAN_NUMBER_MAP = [
+  '', 'C', 'CC', 'CCC', 'CD', 'D', 'DC', 'DCC', 'DCCC', 'CM',
+  '', 'X', 'XX', 'XXX', 'XL', 'L', 'LX', 'LXX', 'LXXX', 'XC',
+  '', 'I', 'II', 'III', 'IV', 'V', 'VI', 'VII', 'VIII', 'IX'
+];
+
+/**
+ * Converts positive integers to (upper case) Roman numerals.
+ * @param {integer} number - The number that should be converted.
+ * @param {boolean} lowerCase - Indicates if the result should be converted
+ *   to lower case letters. The default value is `false`.
+ * @return {string} The resulting Roman number.
+ */
+function toRomanNumerals(number, lowerCase = false) {
+  assert(Number.isInteger(number) && number > 0,
+         'The number should be a positive integer.');
+  let pos, romanBuf = [];
+  // Thousands
+  while (number >= 1000) {
+    number -= 1000;
+    romanBuf.push('M');
+  }
+  // Hundreds
+  pos = (number / 100) | 0;
+  number %= 100;
+  romanBuf.push(ROMAN_NUMBER_MAP[pos]);
+  // Tens
+  pos = (number / 10) | 0;
+  number %= 10;
+  romanBuf.push(ROMAN_NUMBER_MAP[10 + pos]);
+  // Ones
+  romanBuf.push(ROMAN_NUMBER_MAP[20 + number]);
+
+  const romanStr = romanBuf.join('');
+  return (lowerCase ? romanStr.toLowerCase() : romanStr);
+}
+
+export {
+  getLookupTableFactory,
+  MissingDataException,
+  XRefEntryException,
+  XRefParseException,
+  getInheritableProperty,
+  toRomanNumerals,
+};