Replace NULL with nullptr

Also fixed some lines that were too long, and a few other minor
details.

Change-Id: I6efba5fb6e03eb5d0a300fddb2a75bf8e2f175cb
diff --git a/compiler/dex/dataflow_iterator.h b/compiler/dex/dataflow_iterator.h
index 2a06cec..097c2a4 100644
--- a/compiler/dex/dataflow_iterator.h
+++ b/compiler/dex/dataflow_iterator.h
@@ -72,7 +72,7 @@
           : mir_graph_(mir_graph),
             start_idx_(start_idx),
             end_idx_(end_idx),
-            block_id_list_(NULL),
+            block_id_list_(nullptr),
             idx_(0),
             repeats_(0),
             changed_(false) {}