Make SkPictureShader and SkPictureImageFilter use const SkPictures

include/effects/SkPictureImageFilter.h

 /*
  * Copyright 2013 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 SkPictureImageFilter_DEFINED
 #define SkPictureImageFilter_DEFINED
 
 #include "SkImageFilter.h"
 #include "SkPicture.h"
 
 class SK_API SkPictureImageFilter : public SkImageFilter {
 public:
     /**
      *  Refs the passed-in picture.
      */
-    static SkPictureImageFilter* Create(SkPicture* picture) {
+    static SkPictureImageFilter* Create(const SkPicture* picture) {
         return SkNEW_ARGS(SkPictureImageFilter, (picture));
     }
 
     /**
      *  Refs the passed-in picture. cropRect can be used to crop or expand the destination rect when
      *  the picture is drawn. (No scaling is implied by the dest rect; only the CTM is applied.)
      */
-    static SkPictureImageFilter* Create(SkPicture* picture, const SkRect& cropRect) {
+    static SkPictureImageFilter* Create(const SkPicture* picture, const SkRect& cropRect) {
         return SkNEW_ARGS(SkPictureImageFilter, (picture, cropRect));
     }
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkPictureImageFilter)
 
 protected:
-    explicit SkPictureImageFilter(SkPicture* picture);
-    SkPictureImageFilter(SkPicture* picture, const SkRect& cropRect);
+    explicit SkPictureImageFilter(const SkPicture* picture);
+    SkPictureImageFilter(const SkPicture* picture, const SkRect& cropRect);
     virtual ~SkPictureImageFilter();
     /*  Constructs an SkPictureImageFilter object from an SkReadBuffer.
      *  Note: If the SkPictureImageFilter object construction requires bitmap
      *  decoding, the decoder must be set on the SkReadBuffer parameter by calling
      *  SkReadBuffer::setBitmapDecoder() before calling this constructor.
      *  @param SkReadBuffer Serialized picture data.
      */
     explicit SkPictureImageFilter(SkReadBuffer&);
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
     virtual bool onFilterImage(Proxy*, const SkBitmap& src, const Context&,
                                SkBitmap* result, SkIPoint* offset) const SK_OVERRIDE;
     virtual bool onFilterBounds(const SkIRect& src, const SkMatrix&,
                                 SkIRect* dst) const SK_OVERRIDE;
 
 private:
-    SkPicture* fPicture;
-    SkRect     fCropRect;
+    const SkPicture* fPicture;
+    SkRect           fCropRect;
     typedef SkImageFilter INHERITED;
 };
 
 #endif