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

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..30ea7cc1a45a7937d979d0e6170d2febfa5e33e4 100644
--- a/src/image/SkImage_Raster.cpp
+++ b/src/image/SkImage_Raster.cpp
@@ -67,12 +67,12 @@ public:
     SkImage_Raster(const SkImageInfo&, SkData*, size_t rb, SkColorTable*, const SkSurfaceProps*);
     virtual ~SkImage_Raster();
 
-    SkSurface* onNewSurface(const SkImageInfo&, const SkSurfaceProps&) const override;
     bool onReadPixels(const SkImageInfo&, void*, size_t, int srcX, int srcY) const override;
     const void* onPeekPixels(SkImageInfo*, size_t* /*rowBytes*/) const override;
     SkData* onRefEncoded() const override;
     bool getROPixels(SkBitmap*) const override;
     GrTexture* asTextureRef(GrContext*, SkImageUsageType) const override;
+    SkImage* onNewSubset(const SkIRect&) const override;
 
     // exposed for SkSurface_Raster via SkNewImageFromPixelRef
     SkImage_Raster(const SkImageInfo&, SkPixelRef*, const SkIPoint& pixelRefOrigin, size_t rowBytes,
@@ -149,10 +149,6 @@ SkShader* SkImage_Raster::onNewShader(SkShader::TileMode tileX, SkShader::TileMo
     return SkShader::CreateBitmapShader(fBitmap, tileX, tileY, localMatrix);
 }
 
-SkSurface* SkImage_Raster::onNewSurface(const SkImageInfo& info, const SkSurfaceProps& props) const {
-    return SkSurface::NewRaster(info, &props);
-}
-
 bool SkImage_Raster::onReadPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRowBytes,
                                   int srcX, int srcY) const {
     SkBitmap shallowCopy(fBitmap);
@@ -212,6 +208,20 @@ GrTexture* SkImage_Raster::asTextureRef(GrContext* ctx, SkImageUsageType usage)
     return nullptr;
 }
 
+SkImage* SkImage_Raster::onNewSubset(const SkIRect& subset) const {
+    // TODO : could consider heurist of sharing pixels, if subset is pretty close to complete
+
+    SkImageInfo info = SkImageInfo::MakeN32(subset.width(), subset.height(), fBitmap.alphaType());
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRaster(info));
+    if (!surface) {
+        return nullptr;
+    }
+    surface->getCanvas()->clear(0);
+    surface->getCanvas()->drawImage(this, SkIntToScalar(-subset.x()), SkIntToScalar(-subset.y()),
+                                    nullptr);
+    return surface->newImageSnapshot();
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 SkImage* SkImage::NewRasterCopy(const SkImageInfo& info, const void* pixels, size_t rowBytes,