Revert "Rewrite double.parse."

sdk/lib/_internal/compiler/implementation/lib/js_helper.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.
 
 library _js_helper;
 
 import 'dart:collection';
 import 'dart:_foreign_helper' show DART_CLOSURE_TO_JS,
                                    JS,
                                    JS_CALL_IN_ISOLATE,
@@ skipping 257 matching lines @@
     }
     if (match == null) return handleError(source);
     return JS('num', r'parseInt(#, #)', source, radix);
   }
 
   static double parseDouble(String source, double handleError(String source)) {
     checkString(source);
     if (handleError == null) handleError = _throwFormatException;
     // Notice that JS parseFloat accepts garbage at the end of the string.
     // Accept only:
-    // - [+/-]NaN
+    // - NaN
     // - [+/-]Infinity
     // - a Dart double literal
-    // We do allow leading or trailing whitespace.
+    // We do not allow leading or trailing whitespace.
     if (!JS('bool',
-            r'/^\s*[+-]?(?:Infinity|NaN|'
-                r'(?:\.\d+|\d+(?:\.\d*)?)(?:[eE][+-]?\d+)?)\s*$/.test(#)',
+            r'/^\s*(?:NaN|[+-]?(?:Infinity|'
+                r'(?:\.\d+|\d+(?:\.\d+)?)(?:[eE][+-]?\d+)?))\s*$/.test(#)',
             source)) {
       return handleError(source);
     }
     var result = JS('num', r'parseFloat(#)', source);
-    if (result.isNaN) {
-      var trimmed = source.trim();
-      if (trimmed == 'NaN' || trimmed == '+NaN' || trimmed == '-NaN') {
-        return result;
-      }
+    if (result.isNaN && source != 'NaN') {
       return handleError(source);
     }
     return result;
   }
 
   /** [: r"$".codeUnitAt(0) :] */
   static const int DOLLAR_CHAR_VALUE = 36;
 
   /// Creates a string containing the complete type for the class [className]
   /// with the given type arguments.
@@ skipping 1102 matching lines @@
                               expectedArgumentNames);
 }
 
 /**
  * Called by generated code when a static field's initializer references the
  * field that is currently being initialized.
  */
 void throwCyclicInit(String staticName) {
   throw new RuntimeError("Cyclic initialization for static $staticName");
 }