Change signature of SkSpecialImage::draw to take SkScalars

Review URL: https://codereview.chromium.org/1704603002
diff --git a/src/core/SkSpecialSurface.h b/src/core/SkSpecialSurface.h
index 2751c4a..216ef3f 100644
--- a/src/core/SkSpecialSurface.h
+++ b/src/core/SkSpecialSurface.h
@@ -45,6 +45,8 @@
     *  Returns an image of the current state of the surface pixels up to this
     *  point. The canvas returned by 'getCanvas' becomes invalidated by this
     *  call and no more drawing to this surface is allowed.
+    *
+    *  Note: the caller inherits a ref from this call that must be balanced
     */
     SkSpecialImage* newImageSnapshot();