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 4cff5db4c9192884b4b6faa1cf6014a8dccc8074..0c6dd25a2c57cceee3c34cedd92e5ed71437f928 100644
--- a/include/core/SkImage.h
+++ b/include/core/SkImage.h
@@ -8,6 +8,7 @@
 #ifndef SkImage_DEFINED
 #define SkImage_DEFINED
 
+#include "SkFilterQuality.h"
 #include "SkImageInfo.h"
 #include "SkImageEncoder.h"
 #include "SkRefCnt.h"
@@ -128,6 +129,19 @@ 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).

[scroggo, 2015/01/05 16:15:33]

This comment seems to conflict with the code and the comment in the previous
paragraph. This comment appears to state that using a "subset" that is bigger
than this SkImage will return this SkImage (whereas we actually return NULL).

[reed1, 2015/01/05 21:58:14]

Done.

+     */
+    SkImage* newImage(int newWidth, int newHeight, const SkIRect* subset = NULL,
+                      SkFilterQuality = kNone_SkFilterQuality) const;
+
 protected:
     SkImage(int width, int height) :
         fWidth(width),