Update prefservice only if it is available.

components/security_interstitials/content/security_interstitial_page.h

Index: components/security_interstitials/content/security_interstitial_page.h
diff --git a/components/security_interstitials/content/security_interstitial_page.h b/components/security_interstitials/content/security_interstitial_page.h
index 15d28295b24dc019b5895df1c42ba62cbbf375d6..bc68b02dd739a94814e6ffb843f7756fffc82ccc 100644
--- a/components/security_interstitials/content/security_interstitial_page.h
+++ b/components/security_interstitials/content/security_interstitial_page.h
@@ -64,9 +64,6 @@ class SecurityInterstitialPage : public content::InterstitialPageDelegate {
   content::WebContents* web_contents() const;
   GURL request_url() const;
 
-  // Returns the boolean value of the given |pref|.
-  bool IsPrefEnabled(const char* pref);
-
   SecurityInterstitialControllerClient* controller();
 
   MetricsHelper* metrics_helper();