add ImageShader, sharing code with its Bitmap cousin

src/image/SkImage.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkBitmapCache.h"
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkImageGenerator.h"
 #include "SkImagePriv.h"
+#include "SkImageShader.h"
 #include "SkImage_Base.h"
 #include "SkNextID.h"
 #include "SkPixelRef.h"
 #include "SkPixelSerializer.h"
 #include "SkReadPixelsRec.h"
 #include "SkString.h"
 #include "SkSurface.h"
 
 #if SK_SUPPORT_GPU
 #include "GrTexture.h"
@@ skipping 38 matching lines @@
     SkBitmap bm;
     if (as_IB(this)->getROPixels(&bm)) {
         bm.lockPixels();
         bm.unlockPixels();
     }
 }
 
 SkShader* SkImage::newShader(SkShader::TileMode tileX,
                              SkShader::TileMode tileY,
                              const SkMatrix* localMatrix) const {
-    return as_IB(this)->onNewShader(tileX, tileY, localMatrix);
+    return SkImageShader::Create(this, tileX, tileY, localMatrix);
 }
 
 SkData* SkImage::encode(SkImageEncoder::Type type, int quality) const {
     SkBitmap bm;
     if (as_IB(this)->getROPixels(&bm)) {
         return SkImageEncoder::EncodeData(bm, type, quality);
     }
     return nullptr;
 }
 
@@ skipping 282 matching lines @@
 
 SkImage* SkImage::NewFromAdoptedTexture(GrContext*, const GrBackendTextureDesc&, SkAlphaType) {
     return nullptr;
 }
 
 SkImage* SkImage::NewFromTextureCopy(GrContext*, const GrBackendTextureDesc&, SkAlphaType) {
     return nullptr;
 }
 
 #endif