Fix presubmit error introduced by r7221.

TBR=kmillikin@chromium.org

Review URL: http://codereview.chromium.org/6673112

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7223 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.h

@@ -760,7 +760,7 @@ class HBlockEntry: public HTemplateInstruction<0> {
 
 class HDeoptimize: public HControlInstruction {
  public:
-  HDeoptimize(int environment_length)
+  explicit HDeoptimize(int environment_length)
       : HControlInstruction(NULL, NULL),
         values_(environment_length) { }