add SkImageInfo to SkGrPixelRef constructor, to prep for larger CL

BUG=

Review URL: https://codereview.chromium.org/104923011

git-svn-id: http://skia.googlecode.com/svn/trunk/include@12559 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gpu/SkGrPixelRef.h b/gpu/SkGrPixelRef.h
index da4b8fa..c29c27f 100644
--- a/gpu/SkGrPixelRef.h
+++ b/gpu/SkGrPixelRef.h
@@ -47,7 +47,8 @@
      * cache and would like the pixel ref to unlock it in its destructor then transferCacheLock
      * should be set to true.
      */
-    SkGrPixelRef(GrSurface* surface, bool transferCacheLock = false);
+    SkGrPixelRef(GrSurface*, bool transferCacheLock = false);
+    SkGrPixelRef(const SkImageInfo&, GrSurface*, bool transferCacheLock = false);
     virtual ~SkGrPixelRef();
 
     // override from SkPixelRef