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 042107e3e3fcb5ad51eb13d17c84e78e85d61cce..d345202626e42c2cf6062674c431f06952b4c080 100644
--- a/src/image/SkImage_Raster.cpp
+++ b/src/image/SkImage_Raster.cpp
@@ -74,10 +74,6 @@ 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;
 
@@ -138,11 +134,6 @@ 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);
 }