Fix compile errors in legacy copyTo().

include/core/SkBitmap.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkBitmap_DEFINED
 #define SkBitmap_DEFINED
 
@@ skipping 603 matching lines @@
         dimensions is empty, or if there is an unsupported config, false will be
         returned and dst will be untouched.
         @param dst  The bitmap that will be set to a subset of this bitmap
         @param subset The rectangle of pixels in this bitmap that dst will
                       reference.
         @return true if the subset copy was successfully made.
     */
     bool extractSubset(SkBitmap* dst, const SkIRect& subset) const;
 
 #ifdef SK_SUPPORT_LEGACY_COPYTO_CONFIG
-    bool copyTo(SkBitmap* dst, Config c, Allocator* allocator) const;
+    bool copyTo(SkBitmap* dst, Config c, Allocator* allocator = NULL) const;
     bool canCopyTo(Config newConfig) const;
 #endif
     /** Makes a deep copy of this bitmap, respecting the requested colorType,
      *  and allocating the dst pixels on the cpu.
      *  Returns false if either there is an error (i.e. the src does not have
      *  pixels) or the request cannot be satisfied (e.g. the src has per-pixel
      *  alpha, and the requested config does not support alpha).
      *  @param dst The bitmap to be sized and allocated
      *  @param ct The desired colorType for dst
      *  @param allocator Allocator used to allocate the pixelref for the dst
@@ skipping 305 matching lines @@
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 //
 // Helpers until we can fully deprecate SkBitmap::Config
 //
 extern SkBitmap::Config SkColorTypeToBitmapConfig(SkColorType);
 extern SkColorType SkBitmapConfigToColorType(SkBitmap::Config);
 
 #endif