remove unused (by the outside) SkImage::newSurface, and simplify newImage -> newSubset

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 d0cb8d58409375a571af662d399c83875d7a6b08..bbcf182ab8d5c9aca6baa76e65b7ded92ea885ac 100644
--- a/src/image/SkImage_Base.h
+++ b/src/image/SkImage_Base.h
@@ -37,8 +37,6 @@ public:
 
     const SkSurfaceProps& props() const { return fProps; }
 
-    virtual SkSurface* onNewSurface(const SkImageInfo&, const SkSurfaceProps&) const = 0;
-
     virtual const void* onPeekPixels(SkImageInfo*, size_t* /*rowBytes*/) const {
         return nullptr;
     }
@@ -60,9 +58,7 @@ public:
                                   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 SkImage* onNewSubset(const SkIRect&) const = 0;
     virtual SkData* onRefEncoded() const { return nullptr; }
 
     virtual bool onAsLegacyBitmap(SkBitmap*, LegacyBitmapMode) const;