Revert of Revert[2] of add ImageShader, sharing code with its Bitmap cousin

src/image/SkImage_Base.h

Index: src/image/SkImage_Base.h
diff --git a/src/image/SkImage_Base.h b/src/image/SkImage_Base.h
index 757262ad3dc30e0b6643e0b99de612461bf079e5..bbcf182ab8d5c9aca6baa76e65b7ded92ea885ac 100644
--- a/src/image/SkImage_Base.h
+++ b/src/image/SkImage_Base.h
@@ -54,8 +54,11 @@
     // 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; }
+
     virtual SkImage* onNewSubset(const SkIRect&) const = 0;
-
     virtual SkData* onRefEncoded() const { return nullptr; }
 
     virtual bool onAsLegacyBitmap(SkBitmap*, LegacyBitmapMode) const;