Make dart:math strong mode clean.

sdk/lib/math/point.dart

Index: sdk/lib/math/point.dart
diff --git a/sdk/lib/math/point.dart b/sdk/lib/math/point.dart
index 42fcc469eb11de87d10b23764a042e52f1e330cf..01ce93c3b77387774708a0eb0eb25910b4f785a2 100644
--- a/sdk/lib/math/point.dart
+++ b/sdk/lib/math/point.dart
@@ -55,8 +55,9 @@ class Point<T extends num> {
    * it, passing in a double [factor] on a `Point<int>` _causes_ _a_
    * _runtime_ _error_ in checked mode.
    */
-  Point<T> operator *(num factor) {
-    return new Point<T>(x * factor, y * factor);
+  Point<T> operator *(num/*T|int*/ factor) {
+    return new Point<T>(
+        (x * factor) as dynamic/*=T*/, (y * factor) as dynamic/*=T*/);
   }
 
   /**