Fixed check return warnings from Coverity.

chrome/browser/policy/managed_mode_policy_provider.cc

Index: chrome/browser/policy/managed_mode_policy_provider.cc
diff --git a/chrome/browser/policy/managed_mode_policy_provider.cc b/chrome/browser/policy/managed_mode_policy_provider.cc
index e0521679330073a464e82842617f1a545d0c482a..4b09f851af5228a09cade7d409f1345410ae16b6 100644
--- a/chrome/browser/policy/managed_mode_policy_provider.cc
+++ b/chrome/browser/policy/managed_mode_policy_provider.cc
@@ -43,6 +43,8 @@ const base::Value* ManagedModePolicyProvider::GetPolicy(
     const std::string& key) const {
   base::DictionaryValue* dict = GetCachedPolicy();
   base::Value* value = NULL;
+
+  // Returns NULL if the key doesn't exist.
   dict->GetWithoutPathExpansion(key, &value);
   return value;
 }