add ImageShader, sharing code with its Bitmap cousin

src/image/SkImage_Raster.cpp

Index: src/image/SkImage_Raster.cpp
diff --git a/src/image/SkImage_Raster.cpp b/src/image/SkImage_Raster.cpp
index 67498f0e112cf4a5e2f001258906fc6c323316a1..18d6ba6fd7ffecb33342fc530efbcd49912c260f 100644
--- a/src/image/SkImage_Raster.cpp
+++ b/src/image/SkImage_Raster.cpp
@@ -80,10 +80,6 @@ public:
 
     SkPixelRef* getPixelRef() const { return fBitmap.pixelRef(); }
 
-    SkShader* onNewShader(SkShader::TileMode,
-                          SkShader::TileMode,
-                          const SkMatrix* localMatrix) const override;
-
     bool isOpaque() const override;
     bool onAsLegacyBitmap(SkBitmap*, LegacyBitmapMode) const override;
 
@@ -144,11 +140,6 @@ SkImage_Raster::SkImage_Raster(const Info& info, SkPixelRef* pr, const SkIPoint&
 
 SkImage_Raster::~SkImage_Raster() {}
 
-SkShader* SkImage_Raster::onNewShader(SkShader::TileMode tileX, SkShader::TileMode tileY,
-                                      const SkMatrix* localMatrix) const {
-    return SkShader::CreateBitmapShader(fBitmap, tileX, tileY, localMatrix);
-}
-
 SkSurface* SkImage_Raster::onNewSurface(const SkImageInfo& info, const SkSurfaceProps& props) const {
     return SkSurface::NewRaster(info, &props);
 }