Deprecate Math object in corelib in favor of dart:math library.

samples/clock/clock.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library("clock");
 
 #import('dart:html');
+#import('dart:math', prefix: "Math");
 
 #source('balls.dart');
 #source('numbers.dart');
 
 void main() {
   new CountDownClock();
 }
 
 double fpsAverage;
 
@@ skipping 129 matching lines @@
 void setElementPosition(Element elem, double x, double y) {
   elem.style.left = "${x}px";
   elem.style.top = "${y}px";
 }
 
 void setElementSize(Element elem, double l, double t, double r, double b) {
   setElementPosition(elem, l, t);
   elem.style.right = "${r}px";
   elem.style.bottom = "${b}px";
 }