fix spelling in core libraries

sdk/lib/math/rectangle.dart

 // Copyright (c) 2013, 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.
 part of dart.math;
 
 /**
  * A base class for representing two-dimensional axis-aligned rectangles.
  *
  * This rectangle uses a left-handed Cartesian coordinate system, with x
  * directed to the right and y directed down, as per the convention in 2D
  * computer graphics.
  *
  * See also:
  *    [W3C Coordinate Systems Specification](http://www.w3.org/TR/SVG/coords.html#InitialCoordinateSystem).
  *
  * The rectangle is the set of points with representable coordinates greater
  * than or equal to left/top, and with distance to left/top no greater than
- * width/height (to the limit of the precission of the coordinates).
+ * width/height (to the limit of the precision of the coordinates).
  */
 abstract class _RectangleBase<T extends num> {
   const _RectangleBase();
 
   /** The x-coordinate of the left edge. */
   T get left;
   /** The y-coordinate of the top edge. */
   T get top;
   /** The width of the rectangle. */
   T get width;
@@ skipping 238 matching lines @@
 
 /**
  * Converts a negative [int] or [double] to a zero-value of the same type.
  *
  * Returns `0` if value is int, `0.0` if value is double.
  */
 T _clampToZero<T extends num>(T value) {
   assert(value < 0);
   return -value * 0;
 }