Fix for 1267: Implement (partially) Math.pow for integers.

runtime/lib/integers.dart

Index: runtime/lib/integers.dart
===================================================================
--- runtime/lib/integers.dart	(revision 4418)
+++ runtime/lib/integers.dart	(working copy)
@@ -118,7 +118,12 @@
   double toDouble() { return new Double.fromInteger(this); }
 
   int pow(int exponent) {
-    throw "IntegerImplementation.pow not implemented";
+    double res = this.toDouble().pow(exponent);
+    if (res.isInfinite()) {
+      // Use Bigint instead.
+      throw "IntegerImplementation.pow not implemented for large integers.";
+    }
+    return res.toInt();
   }
 
   String toStringAsFixed(int fractionDigits) {
@@ -219,4 +224,8 @@
   int shlFromInt(int other) {
     throw const OutOfMemoryException();
   }
+
+  int pow(int exponent) {
+    throw "Bigint.pow not implemented";
+  }
 }