add ImageShader, sharing code with its Bitmap cousin

src/image/SkImage_Base.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_Base_DEFINED
 #define SkImage_Base_DEFINED
 
@@ skipping 43 matching lines @@
 
     virtual GrTexture* peekTexture() const { return nullptr; }
 
     // return a read-only copy of the pixels. We promise to not modify them,
     // but only inspect them (or encode them).
     virtual bool getROPixels(SkBitmap*) const = 0;
 
     // Caller must call unref when they are done.
     virtual GrTexture* asTextureRef(GrContext*, SkImageUsageType) const = 0;
 
-    virtual SkShader* onNewShader(SkShader::TileMode,
-                                  SkShader::TileMode,
-                                  const SkMatrix* localMatrix) const { return nullptr; }
-
     // newWidth > 0, newHeight > 0, subset either nullptr or a proper subset of this bounds
     virtual SkImage* onNewImage(int newWidth, int newHeight, const SkIRect* subset,
                                 SkFilterQuality) const;
     virtual SkData* onRefEncoded() const { return nullptr; }
 
     virtual bool onAsLegacyBitmap(SkBitmap*, LegacyBitmapMode) const;
 
     virtual bool onIsLazyGenerated() const { return false; }
 
 private:
     const SkSurfaceProps fProps;
 
     typedef SkImage INHERITED;
 };
 
 static inline SkImage_Base* as_IB(SkImage* image) {
     return static_cast<SkImage_Base*>(image);
 }
 
 static inline const SkImage_Base* as_IB(const SkImage* image) {
     return static_cast<const SkImage_Base*>(image);
 }
 
 #endif