Correct comment to refer to SkImageFilter::kReverse_MapDirection.

include/core/SkImageFilter.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageFilter_DEFINED
 #define SkImageFilter_DEFINED
 
@@ skipping 142 matching lines @@
     SkSpecialImage* filterImage(SkSpecialImage* src, const Context&, SkIPoint* offset) const;
 
     enum MapDirection {
         kForward_MapDirection,
         kReverse_MapDirection
     };
     /**
      * Map a device-space rect recursively forward or backward through the
      * filter DAG. kForward_MapDirection is used to determine which pixels of
      * the destination canvas a source image rect would touch after filtering.
-     * kBackward_MapDirection is used to determine which rect of the source
+     * kReverse_MapDirection is used to determine which rect of the source
      * image would be required to fill the given rect (typically, clip bounds).
      * Used for clipping and temp-buffer allocations, so the result need not
      * be exact, but should never be smaller than the real answer. The default
      * implementation recursively unions all input bounds, or returns false if
      * no inputs.
      */
     bool filterBounds(const SkIRect& src, const SkMatrix& ctm, SkIRect* dst,
                       MapDirection = kReverse_MapDirection) const;
 
     /**
@@ skipping 305 matching lines @@
  */
 #define SK_IMAGEFILTER_UNFLATTEN_COMMON(localVar, expectedCount)    \
     Common localVar;                                                \
     do {                                                            \
         if (!localVar.unflatten(buffer, expectedCount)) {           \
             return NULL;                                            \
         }                                                           \
     } while (0)
 
 #endif