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

samples/sunflower/sunflower.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('sunflower');
 
 #import('dart:html');
+#import('dart:math', prefix: 'Math');
 
 final SEED_RADIUS = 2;
 final SCALE_FACTOR = 4;
 final TAU = Math.PI * 2;
 
 final MAX_D = 300;
 final ORANGE = "orange";
 
 num centerX, centerY;
 int seeds = 0;
@@ skipping 46 matching lines @@
   context.strokeStyle = ORANGE;
   context.arc(x, y, SEED_RADIUS, 0, TAU, false);
   context.fill();
   context.closePath();
   context.stroke();
 }
 
 void displaySeedCount(num seedCount) {
   query("#notes").text = "${seedCount} seeds";  
 }