Allow patch files to add top-level declarations to the patched library.

corelib/unified/math/random.dart

Index: corelib/unified/math/random.dart
diff --git a/corelib/unified/math/random.dart b/corelib/unified/math/random.dart
index ee36bf66cd3485680625b72cae2c178e6b1cfb72..efc5678bc69dd711424f659ef01b32cda049a33e 100644
--- a/corelib/unified/math/random.dart
+++ b/corelib/unified/math/random.dart
@@ -8,7 +8,7 @@
  * A random number generator. The default implementation supplies a stream of
  * pseudo-random bits which is not suitable for cryptographic purposes.
  */
-interface Random default _Random {
+class Random {
   /**
    * Creates a random-number generator. The optional parameter [seed] is used
    * to initialize the internal state of the generator. The implementation of
@@ -16,7 +16,7 @@ interface Random default _Random {
    *
    * Implementation note: The default implementation uses up to 64-bits of seed.
    */
-  Random([int seed]);
+  external factory Random([int seed]);
 
   /**
    * Generates a positive random integer uniformly distributed on the range
@@ -25,23 +25,16 @@ interface Random default _Random {
    * Implementation note: The default implementation supports [max] values
    * between 1 and ((1<<32) - 1) inclusive.
    */
-  int nextInt(int max);
+  abstract int nextInt(int max);
 
   /**
    * Generates a positive random floating point value uniformly distributed on
    * the range from 0.0, inclusive, to 1.0, exclusive.
    */
-  double nextDouble();
+  abstract double nextDouble();
 
   /**
    * Generates a random boolean value.
    */
-  bool nextBool();
-}
-
-class _Random implements Random {
-  external _Random([int seed = null]);
-  external int nextInt(int max);
-  external double nextDouble();
-  external bool nextBool();
+  abstract bool nextBool();
 }