Remove offset to SkMallocPixelRef::NewWithData - use SkData::NewSubset instead.

R=scroggo@google.com, mtklein@google.com, reed@google.com

Author: halcanary@google.com

Review URL: https://codereview.chromium.org/243483002

git-svn-id: http://skia.googlecode.com/svn/trunk@14289 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/dm/DMWriteTask.cpp b/dm/DMWriteTask.cpp
index 890a4bb..f7fa014 100644
--- a/dm/DMWriteTask.cpp
+++ b/dm/DMWriteTask.cpp
@@ -84,8 +84,11 @@
         }
 
         const size_t offset = data->size() - bitmapBytes;
+        SkAutoTUnref<SkData> subset(
+                SkData::NewSubset(data, offset, bitmapBytes));
         SkAutoTUnref<SkPixelRef> pixels(
-            SkMallocPixelRef::NewWithData(info, rowBytes, NULL/*ctable*/, data, offset));
+            SkMallocPixelRef::NewWithData(
+                    info, rowBytes, NULL/*ctable*/, subset));
         SkASSERT(pixels);
 
         bitmap->setConfig(info, rowBytes);