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/mir_field_info.h b/compiler/dex/mir_field_info.h
index 11773e7..e4570fd 100644
--- a/compiler/dex/mir_field_info.h
+++ b/compiler/dex/mir_field_info.h
@@ -124,7 +124,7 @@
   uint16_t declaring_field_idx_;
   // The type index of the class declaring the field, 0 if unresolved.
   uint16_t declaring_class_idx_;
-  // The dex file that defines the class containing the field and the field, nullptr if unresolved.
+  // The dex file that defines the class containing the field and the field, null if unresolved.
   const DexFile* declaring_dex_file_;
 };