Fix NULL deref in safe browsing preference validation delegate.

chrome/browser/prefs/tracked/tracked_preference_validation_delegate.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PREFS_TRACKED_TRACKED_PREFERENCE_VALIDATION_DELEGATE_H_
 #define CHROME_BROWSER_PREFS_TRACKED_TRACKED_PREFERENCE_VALIDATION_DELEGATE_H_
 
 #include <string>
 #include <vector>
 
 #include "chrome/browser/prefs/pref_hash_store_transaction.h"
 #include "chrome/browser/prefs/tracked/tracked_preference_helper.h"
 
 namespace base {
 class DictionaryValue;
 class Value;
 }
 
 // A TrackedPreferenceValidationDelegate is notified of the results of each
 // tracked preference validation event.
 class TrackedPreferenceValidationDelegate {
  public:
   virtual ~TrackedPreferenceValidationDelegate() {}
 
   // Notifies observes of the result (|value_state|) of checking the atomic
-  // |value| at |pref_path|. |reset_action| indicates whether or not a reset
-  // will occur based on |value_state| and the enforcement level in place.
+  // |value| (which may be NULL) at |pref_path|. |reset_action| indicates
+  // whether or not a reset will occur based on |value_state| and the
+  // enforcement level in place.
   virtual void OnAtomicPreferenceValidation(
       const std::string& pref_path,
       const base::Value* value,
       PrefHashStoreTransaction::ValueState value_state,
       TrackedPreferenceHelper::ResetAction reset_action) = 0;
 
   // Notifies observes of the result (|value_state|) of checking the split
-  // |dict_value| at |pref_path|. |reset_action| indicates whether or not a
-  // reset of |value_keys| will occur based on |value_state| and the enforcement
-  // level in place.
+  // |dict_value| (which may be NULL) at |pref_path|. |reset_action| indicates
+  // whether or not a reset of |value_keys| will occur based on |value_state|
+  // and the enforcement level in place.
   virtual void OnSplitPreferenceValidation(
       const std::string& pref_path,
       const base::DictionaryValue* dict_value,
       const std::vector<std::string>& invalid_keys,
       PrefHashStoreTransaction::ValueState value_state,
       TrackedPreferenceHelper::ResetAction reset_action) = 0;
 };
 
 #endif  // CHROME_BROWSER_PREFS_TRACKED_TRACKED_PREFERENCE_VALIDATION_DELEGATE_H_