add newImage API

include/core/SkImage.h

Index: include/core/SkImage.h
diff --git a/include/core/SkImage.h b/include/core/SkImage.h
index 6070b6bf6bfefdd50ba5bc07ca8e118f54ef9165..2bb5e029a2b1d39649d6faec4b8a00c90695d458 100644
--- a/include/core/SkImage.h
+++ b/include/core/SkImage.h
@@ -124,6 +124,18 @@ public:
      */
     SkSurface* newSurface(const SkImageInfo&, const SkSurfaceProps* = NULL) const;
 
+    /**
+     *  Return an image that is a rescale of this image (using newWidth, newHeight).
+     *
+     *  If subset is NULL, then the entire original image is used as the src for the scaling.
+     *  If subset is not NULL, then it specifies subset of src-pixels used for scaling. If
+     *  subset extends beyond the bounds of the original image, then NULL is returned.
+     *
+     *  Note: it is legal for the returned image to be the same instance as the src image
+     *  (if the new dimensions == the src dimensions and any subset encloses the entire src).
+     */
+    SkImage* newImage(int newWidth, int newHeight, const SkIRect* subset = NULL) const;

[scroggo, 2014/12/22 22:08:27]

For use by Android, it might be nice to be able to have an option to supply the
memory for pixels - or, to let them know how much was used, if we can convince
them to let us use a native allocation (see
https://docs.google.com/document/d/1Axl4VtjxX5kAwX87mLFzni8Ii4Cnsr7BFMsaWY9vF...).
(I suppose in that case, they can use SkImageInfo::minRowBytes().)

[reed2, 2014/12/24 19:47:26]

For GPU images, it is hard to see how to supply the memory. For CPU images, I
guess we could add an optional allocator callback. It seems more uniform and
cleaner if we can augment the VM so we can annotate ALL of our large allocations
so that Android apps can know where their memory went (not just some images).

[scroggo, 2014/12/30 11:04:40]

Agreed. The more I think about it, the more I think annotating native
allocations is the right way to go. When I talked to Derek about it last week,
his plan was to work with the VM team to get something added, but at the time he
had not heard anything yet.

+
 protected:
     SkImage(int width, int height) :
         fWidth(width),