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/samplecode/SampleDitherBitmap.cpp b/samplecode/SampleDitherBitmap.cpp
index 676d4c3..bdd3071 100644
--- a/samplecode/SampleDitherBitmap.cpp
+++ b/samplecode/SampleDitherBitmap.cpp
@@ -56,12 +56,9 @@
     for (int i = 0; i < 256; i++) {
         c[i] = SkPackARGB32(0xFF, i, 0, 0);
     }
-    SkColorTable* ctable = new SkColorTable(c, 256);
-
     SkBitmap bm;
     bm.allocPixels(SkImageInfo::Make(256, 32, kIndex_8_SkColorType, kPremul_SkAlphaType),
-                   nullptr, ctable);
-    ctable->unref();
+                   SkColorTable::Make(c, 256));
 
     bm.lockPixels();
     for (int y = 0; y < bm.height(); y++) {