clean up (partially) colortable api

Needs this to land: https://codereview.chromium.org/2789853002/

Bug: skia:
Change-Id: I38d916a546b7fa64d000d973e695ddda24a589e7
Reviewed-on: https://skia-review.googlesource.com/10600
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>
diff --git a/bench/BitmapBench.cpp b/bench/BitmapBench.cpp
index 8e881a6..fdf17e9 100644
--- a/bench/BitmapBench.cpp
+++ b/bench/BitmapBench.cpp
@@ -44,10 +44,8 @@
             }
         }
     }
-    SkColorTable* ctable = new SkColorTable(storage, 216);
     dst->allocPixels(SkImageInfo::Make(src.width(), src.height(), kIndex_8_SkColorType, aType),
-                     nullptr, ctable);
-    ctable->unref();
+                     SkColorTable::Make(storage, 216));
 
     SkAutoLockPixels alps(src);
     SkAutoLockPixels alpd(*dst);