Move JSSyntaxRegExp to core as a private member. This removes the last refrences to dart:coreimpl.

runtime/lib/regexp_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+patch class RegExp {
+  /* patch */ factory RegExp(String pattern,
+                             {bool multiLine: false,
+                              bool ignoreCase: false}) {
+    return new _JSSyntaxRegExp(pattern,
+                               multiLine: multiLine,
+                               ignoreCase: ignoreCase);
+  }
+}
+
 class _JSRegExpMatch implements Match {
   _JSRegExpMatch(this.regexp, this.str, this._match);
 
   int get start => _start(0);
   int get end => _end(0);
 
   int _start(int groupIdx) {
     return _match[(groupIdx * MATCH_PAIR)];
   }
 
   int _end(int groupIdx) {
     return _match[(groupIdx * MATCH_PAIR) + 1];
   }
 
   String group(int groupIdx) {
     if (groupIdx < 0 || groupIdx > regexp._groupCount) {
       throw new RangeError.value(groupIdx);
     }
     int startIndex = _start(groupIdx);
     int endIndex = _end(groupIdx);
     if (startIndex == -1) {
       assert(endIndex == -1);
       return null;
     }
-    // TODO(ajohnsen): Use _substringUnchecked when regexp is in core.
-    return str.substring(startIndex, endIndex);
+    return str._substringUnchecked(startIndex, endIndex);
   }
 
   String operator [](int groupIdx) {
     return this.group(groupIdx);
   }
 
   List<String> groups(List<int> groupsSpec) {
     var groupsList = new List<String>(groupsSpec.length);
     for (int i = 0; i < groupsSpec.length; i++) {
       groupsList[i] = group(groupsSpec[i]);
     }
     return groupsList;
   }
 
   int get groupCount => regexp._groupCount;
 
   String get pattern => regexp.pattern;
 
   final RegExp regexp;
   final String str;
   final List<int> _match;
   static const int MATCH_PAIR = 2;
 }
 
 
-patch class JSSyntaxRegExp {
-  /* patch */ factory JSSyntaxRegExp(
+class _JSSyntaxRegExp implements RegExp {
+  factory _JSSyntaxRegExp(
       String pattern,
       {bool multiLine: false,
        bool ignoreCase: false}) native "JSSyntaxRegExp_factory";
 
-  /* patch */ Match firstMatch(String str) {
+  Match firstMatch(String str) {
     List match = _ExecuteMatch(str, 0);
     if (match == null) {
       return null;
     }
     return new _JSRegExpMatch(this, str, match);
   }
 
-  /* patch */ Iterable<Match> allMatches(String str) {
+  Iterable<Match> allMatches(String str) {
     List<Match> result = new List<Match>();
     int length = str.length;
     int startIndex = 0;
     while (true) {
       List match = _ExecuteMatch(str, startIndex);
       if (match == null) {
         break;
       }
       result.add(new _JSRegExpMatch(this, str, match));
       int endIndex = match[1];
       if (endIndex == length) {
         break;
       } else if (match[0] == endIndex) {
         ++startIndex;  // empty match, advance and restart
       } else {
         startIndex = endIndex;
       }
     }
     return result;
   }
 
-  /* patch */ bool hasMatch(String str) {
+  bool hasMatch(String str) {
     List match = _ExecuteMatch(str, 0);
     return (match == null) ? false : true;
   }
 
-  /* patch */ String stringMatch(String str) {
+  String stringMatch(String str) {
     List match = _ExecuteMatch(str, 0);
     if (match == null) {
       return null;
     }
-    // TODO(ajohnsen): Use _substringUnchecked when regexp is in core.
-    return str.substring(match[0], match[1]);
+    return str._substringUnchecked(match[0], match[1]);
   }
 
-  /* patch */ String get pattern native "JSSyntaxRegExp_getPattern";
+  String get pattern native "JSSyntaxRegExp_getPattern";
 
-  /* patch */ bool get multiLine native "JSSyntaxRegExp_multiLine";
+  bool get multiLine native "JSSyntaxRegExp_multiLine";
 
-  /* patch */ bool get ignoreCase native "JSSyntaxRegExp_ignoreCase";
+  bool get ignoreCase native "JSSyntaxRegExp_ignoreCase";
 
   int get _groupCount native "JSSyntaxRegExp_getGroupCount";
 
   List _ExecuteMatch(String str, int start_index)
       native "JSSyntaxRegExp_ExecuteMatch";
 }