Factor and simplify generation of the lookup trie used for HTMLLookupTrie.

third_party/WebKit/Source/build/scripts/trie_builder.py

+# Copyright 2016 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.
+
+from collections import defaultdict
+
+
+def _single_trie(string_to_value_pairs, index):
+    """Build a single trie from a dict of input string to output values.
+
+    This function assumes that all of the strings in
+    string_to_value_pairs have the same length.
+    The input
+    {'abcd': 'ABCD', 'adef': 'ADEF', 'adeg': 'ADEG'}
+    creates a trie like this:
+    {
+     'a' : {
+      'b': {'cd' : "ABCD"},
+      'd' : {
+       'e' : {
+        'f' : {'': "ADEF"},
+        'g' : {'': "ADEG"},
+       },
+      },
+     },
+    }
+    """
+    dicts_by_indexed_letter = defaultdict(list)
+    for string, value in string_to_value_pairs:
+        dicts_by_indexed_letter[string[index]].append((string, value))
+
+    output = {}
+    for char, d in dicts_by_indexed_letter.items():
+        if len(d) == 1:
+            string = d[0][0]
+            value = d[0][1]
+            output[char] = {string[index + 1:]: value}
+        else:
+            output[char] = _single_trie(d, index + 1)
+
+    return output
+
+
+def trie_list_by_str_length(str_to_return_value_dict):
+    """Make a list of tries from a dict of input string to output value.
+
+    All strings should be all lower case.
+    """
+    dicts_by_length = defaultdict(list)
+    for string, value in str_to_return_value_dict.items():
+        dicts_by_length[len(string)].append((string, value))
+
+    output = []
+    for length, pairs in dicts_by_length.items():
+        output.append((length, _single_trie(sorted(pairs), 0)))
+
+    return output