Pixels class prototype and test (not to be committed).

sdk/lib/core/num.dart

Index: sdk/lib/core/num.dart
diff --git a/sdk/lib/core/num.dart b/sdk/lib/core/num.dart
index 21f23eef18321ab7fc4b59aa397cdbb7ead0b0d6..f21be37f6c841d4921f55d15c83a6e812f2280fa 100644
--- a/sdk/lib/core/num.dart
+++ b/sdk/lib/core/num.dart
@@ -106,7 +106,7 @@ abstract class num implements Comparable<num> {
   num operator %(num other);
 
   /** Division operator. */
-  double operator /(num other);
+  num operator /(num other);
 
   /**
    * Truncating division operator.
@@ -311,6 +311,9 @@ abstract class num implements Comparable<num> {
    */
   double toDouble();
 
+  /** Return this [num] as a [pixels].  */
+  pixels toPixels();
+
   /**
    * Returns a decimal-point string-representation of `this`.
    *