Add SkSpecialImage::makeTextureImage entry point & update filterInput

src/core/SkSpecialImage.h

Index: src/core/SkSpecialImage.h
diff --git a/src/core/SkSpecialImage.h b/src/core/SkSpecialImage.h
index 1a01a5abc7a8a285955df101aa67ac759ab73775..47ad6ccab7972f7de6e2d698fc5f978d910963bc 100644
--- a/src/core/SkSpecialImage.h
+++ b/src/core/SkSpecialImage.h
@@ -14,12 +14,16 @@
 // remove this when internal_getProxy goes away (see skbug.com/4965)
 #include "SkImageFilter.h"
 
+#include "SkImageInfo.h" // for SkAlphaType
+
+class GrContext;
 class GrTexture;
 class SkBitmap;
 class SkCanvas;
 class SkImage;
 struct SkImageInfo;
 class SkPaint;
+class SkPixmap;
 class SkSpecialSurface;
 
 enum {
@@ -51,6 +55,13 @@ public:
     virtual size_t getSize() const = 0;
 
     /**
+     *  Ensures that a special image is backed by a texture (when GrContext is non-null). If no
+     *  transformation is required, the returned image may be the same as this special image.
+     *  If this special image is from a different GrContext, this will fail.
+     */
+    sk_sp<SkSpecialImage> makeTextureImage(SkImageFilter::Proxy*, GrContext*);
+
+    /**
      *  Draw this SpecialImage into the canvas.
      */
     void draw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*) const;