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

lib/core/int.dart

Index: lib/core/int.dart
diff --git a/lib/core/int.dart b/lib/core/int.dart
index 404d10a4d091f81490fc811fb50656c231802dcf..0855a62b6346bc89cb0e7dedec350eb5107e8f22 100644
--- a/lib/core/int.dart
+++ b/lib/core/int.dart
@@ -24,4 +24,20 @@ abstract class int implements num {
   int floor();
   int ceil();
   int truncate();
+  /**
+   * Returns a representation of this [int] value.
+   *
+   * It should always be the case that if 'i' is an [int] value, then
+   * [:i == int.parse(i.toString())].
+   */
+  String toString();
+
+  /**
+   * Parse [source] as an integer literal and return its value.
+   *
+   * Accepts "0x" prefix for hexadecimal numbers, otherwise defaults
+   * to base-10.
+   * Throws a [FormatException] if [source] is not a valid integer literal.
+   */
+  external static int parse(String source);
 }