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

lib/core/double.dart

Index: lib/core/double.dart
diff --git a/lib/core/double.dart b/lib/core/double.dart
index bf6a19a7de10bf83b9476a126f0632d367b14a8e..a1c47d46e510a08f68e8237c4e59f745d0ee1b4c 100644
--- a/lib/core/double.dart
+++ b/lib/core/double.dart
@@ -8,7 +8,7 @@
 // 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;
@@ -28,4 +28,31 @@ abstract class double implements num {
   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);
 }