mark all SkImage methods const, so we can make it thread-safe

include/core/SkImage.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_DEFINED
 #define SkImage_DEFINED
 
@@ skipping 44 matching lines @@
      * Return the GrTexture that stores the image pixels. Calling getTexture
      * does not affect the reference count of the GrTexture object.
      * Will return NULL if the image does not use a texture.
      */
     GrTexture* getTexture();
 
     virtual SkShader* newShader(SkShader::TileMode,
                                 SkShader::TileMode,
                                 const SkMatrix* localMatrix = NULL) const;
 
-    void draw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*);
+    void draw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*) const;
 
     /**
      *  Draw the image, cropped to the src rect, to the dst rect of a canvas.
      *  If src is larger than the bounds of the image, the rest of the image is
      *  filled with transparent black pixels.
      *
      *  See SkCanvas::drawBitmapRectToRect for similar behavior.
      */
-    void draw(SkCanvas*, const SkRect* src, const SkRect& dst, const SkPaint*);
+    void draw(SkCanvas*, const SkRect* src, const SkRect& dst, const SkPaint*) const;
 
     /**
      *  If the image has direct access to its pixels (i.e. they are in local
      *  RAM) return the (const) address of those pixels, and if not null, return
      *  the ImageInfo and rowBytes. The returned address is only valid while
      *  the image object is in scope.
      *
      *  On failure, returns NULL and the info and rowBytes parameters are
      *  ignored.
      */
@@ skipping 46 matching lines @@
      *  On failure, false will be returned, and bitmap will unmodified.
      */
     // On ice for now:
     // - should it respect the particular colortype/alphatype of the src
     // - should it have separate entrypoints for preallocated and not bitmaps?
     // - isn't it enough to allow the caller to draw() the image into a canvas?
     bool readPixels(SkBitmap* bitmap, const SkIRect* subset = NULL) const;
 };
 
 #endif