Update to Dart 2.20

Note that the dart2js speedtest just crashed from 1.6s to 25s.  No change in the dart VM speedtest.
Also, the unit tests currently don’t run due to stricter package rules (however, if the packages are hacked, the unit tests all pass).

Author: NeilFraser

dart/DMPClass.dart

@@ -1446,9 +1446,9 @@ class DiffMatchPatch {
    * Returns the best match index or -1.
    */
   int _match_bitap(String text, String pattern, int loc) {
-    Expect.isTrue(Match_MaxBits == 0 || pattern.length <= Match_MaxBits,
-        'Pattern too long for this application.');
-
+    if (Match_MaxBits != 0 && pattern.length > Match_MaxBits) {
+      throw new Exception('Pattern too long for this application.');
+    }
     // Initialise the alphabet.
     Map<String, int> s = _match_alphabet(pattern);
 
@@ -1967,7 +1967,7 @@ class DiffMatchPatch {
         }
         while (!bigpatch.diffs.isEmpty &&
             patch.length1 < patch_size - Patch_Margin) {
-          int diff_type = bigpatch.diffs[0].operation;
+          Operation diff_type = bigpatch.diffs[0].operation;
           String diff_text = bigpatch.diffs[0].text;
           if (diff_type == Operation.insert) {
             // Insertions are harmless.

dart/DiffMatchPatch.dart

@@ -19,6 +19,7 @@
 library DiffMatchPatch;
 
 import 'dart:math';
+import 'dart:collection';
 
 part 'DMPClass.dart';
 part 'DiffClass.dart';

dart/tests/DiffMatchPatchTest.dart

@@ -72,13 +72,13 @@ class Expect {
   static void mapEquals(Map expected, Map actual, String msg) {
     for (var k in actual.keys) {
       if (!expected.containsKey(k)) {
-        throw new Exception('Expect.mapEquals(unexpected key <$key> found '
+        throw new Exception('Expect.mapEquals(unexpected key <$k> found '
             'expected: <$expected>, actual: <$actual> $msg) fails');
       }
     }
     for (var k in expected.keys) {
       if (!actual.containsKey(k)) {
-        throw new Exception('Expect.mapEquals(key <$key> not found '
+        throw new Exception('Expect.mapEquals(key <$k> not found '
             'expected: <$expected>, actual: <$actual> $msg) fails');
       }
       Expect.equals(actual[k], expected[k], "$msg [Key: $k]");

dart/tests/Speedtest.dart

@@ -5,8 +5,10 @@ import '../DiffMatchPatch.dart';
 // dart2js --out=Speedtest.dart.js Speedtest.dart
 
 void launch(Event e) {
-  String text1 = document.query('#text1').value;
-  String text2 = document.query('#text2').value;
+  HtmlElement input1 = document.getElementById('text1');
+  HtmlElement input2 = document.getElementById('text2');
+  String text1 = input1.text;
+  String text2 = input2.text;
 
   DiffMatchPatch dmp = new DiffMatchPatch();
   dmp.Diff_Timeout = 0.0;
@@ -17,12 +19,11 @@ void launch(Event e) {
   DateTime date_end = new DateTime.now();
 
   var ds = dmp.diff_prettyHtml(d);
-  document.query('#outputdiv').setInnerHtml(
+  document.getElementById('outputdiv').setInnerHtml(
       '$ds<BR>Time: ${date_end.difference(date_start)} (h:mm:ss.mmm)');
 }
 
 void main() {
-  document.query('#launch').addEventListener('click', launch);
-  document.query('#outputdiv').setInnerHtml('');
+  document.getElementById('launch').addEventListener('click', launch);
+  document.getElementById('outputdiv').setInnerHtml('');
 }
-