Allow client to force an SkImage snapshot to be unique (and uniquely own its backing store).

include/core/SkSurface.h

Index: include/core/SkSurface.h
diff --git a/include/core/SkSurface.h b/include/core/SkSurface.h
index 45262d78e63d3d30351c43ccd22ae3c2442ad0a3..fcbc1bfcec81c6786b30ce1a4dcb9c220debf1ce 100644
--- a/include/core/SkSurface.h
+++ b/include/core/SkSurface.h
@@ -228,13 +228,24 @@ public:
     SkSurface* newSurface(const SkImageInfo&);
 
     /**
+     * In rare instances a client may want a unique copy of the SkSurface's contents in an image
+     * snapshot. This enum can be used to enforce that the image snapshot's backing store is not
+     * shared with another image snapshot or the surface's backing store. This is generally more
+     * expensive.
+     */
+    enum ForceUnique {
+        kNo_ForceUnique,
+        kYes_ForceUnique
+    };
+
+    /**
      *  Returns an image of the current state of the surface pixels up to this
      *  point. Subsequent changes to the surface (by drawing into its canvas)
      *  will not be reflected in this image. If a copy must be made the Budgeted
      *  parameter controls whether it counts against the resource budget
      *  (currently for the gpu backend only).
      */
-    SkImage* newImageSnapshot(Budgeted = kYes_Budgeted);
+    SkImage* newImageSnapshot(Budgeted = kYes_Budgeted, ForceUnique = kNo_ForceUnique);

[reed1, 2016/02/15 21:32:13]

Crud. I think its cruddy when we have more than one default arg. I had forgotten
that we had budgeted. I wonder if we should just have a 2nd version that
explicitly requires both enums..?

 
     /**
      *  Though the caller could get a snapshot image explicitly, and draw that,