Move parseInt parseDouble to int/double classes as a static method.

lib/core/double.dart

 // Copyright (c) 2011, 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.
 
 // Dart core library.
 
 // TODO: Convert this abstract class into a concrete class double
 // that uses the patch class functionality to account for the
 // different platform implementations.
 
-abstract class double implements num {
+abstract class double extends num {
   static const double NAN = 0.0 / 0.0;
   static const double INFINITY = 1.0 / 0.0;
   static const double NEGATIVE_INFINITY = -INFINITY;
 
   // Specialization of super-interface. Double is contagious. We can therefore
   // specialize more methods than in other num sub-interfaces.
   abstract double remainder(num other);
   abstract double operator +(num other);
   abstract double operator -(num other);
   abstract double operator *(num other);
   abstract double operator %(num other);
   abstract double operator /(num other);
   abstract double operator ~/(num other);
   abstract double operator -();
   abstract double abs();
   abstract double round();
   abstract double floor();
   abstract double ceil();
   abstract double truncate();
+
+  /**
+   * Provide a representation of this [double] value.
+   *
+   * The representation is a number literal such that the closest double value
+   * to the representation's mathematical value is this [double].
+   *
+   * Returns "NaN" for the Not-a-Number value.
+   * Returns "Infinity" and "-Infinity" for positive and negative Infinity.
+   * Returns "-0.0" for negative zero.
+   *
+   * It should always be the case that if [:d:] is a [double], then
+   * [:d == double.parse(d.toString()):].
+   */
+  abstract String toString();
+
+  /**
+   * Parse [source] as an double literal and return its value.
+   *
+   * Accepts the same format as double literals:
+   *   [: ['+'|'-'] [digit* '.'] digit+ [('e'|'E') ['+'|'-'] digit+] :]
+   *
+   * Also recognizes "NaN", "Infinity" and "-Infinity" as inputs and returns the
+   * corresponding double value.
+   * Throws a [FormatException] if [source] is not a valid double literal.
+   */
+  external static double parse(String source);
 }