Introduce cross_site_iframe_factory.html, and use it in a test

content/test/data/tree_parser_util.js

Index: content/test/data/tree_parser_util.js
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+// Copyright 2015 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.
+
+/**
+ * Parser for a simple grammar that describes a tree structure using a function-
+ * like "a(b(c,d))" syntax. Original intended usage: to have browsertests
+ * specify an arbitrary tree of iframes, loaded from various sites, without
+ * having to write a .html page for each level or do crazy feats of data: url
+ * escaping. But there's nothing really iframe-specific here. See below for some
+ * examples of the grammar and the parser output.
+ *
+ * @example <caption>Basic syntax: an identifier followed by arg list.</caption>
+ * TreeParserUtil.parse('abc ()');  // returns { value: 'abc', children: [] }
+ *
+ * @example <caption>The arg list is optional. Dots are legal in ids.</caption>
+ * TreeParserUtil.parse('b.com');  // returns { value: 'b.com', children: [] }
+ *
+ * @example <caption>Commas separate children in the arg list.</caption>
+ * // returns { value: 'b', children: [
+ * //           { value: 'c', children: [] },
+ * //           { value: 'd', children: [] }
+ * //         ]}
+ * TreeParserUtil.parse('b (c, d)';
+ *
+ * @example <caption>Children can have children, and so on.</caption>
+ * // returns { value: 'e', children: [
+ * //           { value: 'f', children: [
+ * //             { value: 'g', children: [
+ * //               { value: 'h', children: [] },
+ * //               { value: 'i', children: [
+ * //                 { value: 'j', children: [] }
+ * //               ]},
+ * //             ]}
+ * //           ]}
+ * //         ]}
+ * TreeParserUtil.parse('e(f(g(h(),i(j))))';
+ *
+ * @example <caption>flatten() converts a [sub]tree back to a string.</caption>
+ * var tree = TreeParserUtil.parse('b.com (c.com(e.com), d.com)');
+ * TreeParserUtil.flatten(tree.children[0]);  // returns 'c.com(e.com())'
+ */
+var TreeParserUtil = (function() {
+  'use strict';
+
+  /**
+   * Parses an input string into a tree. See class comment for examples.
+   * @returns A tree of the form {value: <string>, children: <Array.<tree>>}.
+   */
+  function parse(input) {
+    var tokenStream = lex(input);
+
+    var result = takeIdAndChild(tokenStream);
+    if (tokenStream.length != 0)
+      throw new Error('Expected end of stream, but found "' +
+                      tokenStream[0] + '".')
+    return result;
+  }
+
+  /**
+   * Inverse of |parse|. Converts a parsed tree object into a string. Can be
+   * used to forward a subtree as an argument to a nested document.
+   */
+  function flatten(tree) {
+    return tree.value + '(' + tree.children.map(flatten).join(',') + ')';
+  }
+
+  /**
+   * Lexer function to convert an input string into a token stream.  Splits the
+   * input along whitespace, parens and commas. Whitespace is removed, while
+   * parens and commas are preserved as standalone tokens.
+   *
+   * @param {string} input The input string.
+   * @return {Array.<string>} The resulting token stream.
+   */
+  function lex(input) {
+    return input.split(/(\s+|\(|\)|,)/).reduce(
+      function (resultArray, token) {
+        var trimmed = token.trim();
+        if (trimmed) {
+          resultArray.push(trimmed);
+        }
+        return resultArray;
+      }, []);
+  }
+
+
+  /**
+   * Consumes from the stream an identifier and optional child list, returning
+   * its parsed representation.
+   */
+  function takeIdAndChild(tokenStream) {
+    return { value: takeIdentifier(tokenStream),
+             children: takeChildList(tokenStream) };
+  }
+
+  /**
+   * Consumes from the stream an identifier, returning its value (as a string).
+   */
+  function takeIdentifier(tokenStream) {
+    if (tokenStream.length == 0)
+      throw new Error('Expected an identifier, but found end-of-stream.');
+    var token = tokenStream.shift();
+    if (!token.match(/[a-zA-Z0-9.-]+/))
+      throw new Error('Expected an identifier, but found "' + token + '".');
+    return token;
+  }
+
+  /**
+   * Consumes an optional child list from the token stream, returning a list of
+   * the parsed children.
+   */
+  function takeChildList(tokenStream) {
+    // Remove the next token from the stream if it matches |token|.
+    function tryToEatA(token) {
+      if (tokenStream[0] == token) {
+        tokenStream.shift();
+        return true;
+      }
+      return false;
+    }
+
+    // Bare identifier case, as in 'b' in the input '(a (b, c))'
+    if (!tryToEatA('('))
+      return [];
+
+    // Empty list case, as in 'b' in the input 'a (b (), c)'.
+    if (tryToEatA(')')) {
+      return [];
+    }
+
+    // List with at least one entry.
+    var result = [ takeIdAndChild(tokenStream) ];
+
+    // Additional entries allowed with commas.
+    while (tryToEatA(',')) {
+      result.push(takeIdAndChild(tokenStream));
+    }
+
+    // End of list.
+    if (tryToEatA(')')) {
+      return result;
+    }
+    if (tokenStream.length == 0)
+      throw new Error('Expected ")" or ",", but found end-of-stream.');
+    throw new Error('Expected ")" or ",", but found "' + tokenStream[0] + '".');
+  }
+
+  return {
+    parse:   parse,
+    flatten: flatten
+  };
+})();