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/pass_driver.h b/compiler/dex/pass_driver.h
index 671bcec..8762b53 100644
--- a/compiler/dex/pass_driver.h
+++ b/compiler/dex/pass_driver.h
@@ -68,7 +68,7 @@
    * @return whether the pass was applied.
    */
   virtual bool RunPass(const char* pass_name) {
-    // Paranoid: c_unit cannot be nullptr and we need a pass name.
+    // Paranoid: c_unit cannot be null and we need a pass name.
     DCHECK(pass_name != nullptr);
     DCHECK_NE(pass_name[0], 0);