Pass the previous and the current PolicyMap to Observers of the PolicyService.

chrome/browser/policy/policy_service_impl.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/policy/policy_service_impl.h"
 
 #include "base/observer_list.h"
 #include "base/stl_util.h"
 
 namespace policy {
@@ skipping 107 matching lines @@
       it->second->policies.empty() &&
       it->second->observers.size() == 0) {
     delete it->second;
     entries_.erase(it);
   }
 }
 
 void PolicyServiceImpl::MergeAndTriggerUpdates() {
   // TODO(joaodasilva): do this for each namespace once the providers also
   // provide policy for more namespaces.
-  PolicyMap new_policies;
+  PolicyMap policies;
   for (ProviderList::iterator it = providers_.begin();
        it != providers_.end(); ++it) {
-    new_policies.MergeFrom((*it)->policies);
+    policies.MergeFrom((*it)->policies);
   }
 
   Entry* entry = GetOrCreate(std::make_pair(POLICY_DOMAIN_CHROME, ""));
-  if (!new_policies.Equals(entry->policies)) {
-    entry->policies.Swap(&new_policies);
-    FOR_EACH_OBSERVER(PolicyService::Observer,
-                      entry->observers,
-                      OnPolicyUpdated(POLICY_DOMAIN_CHROME, ""));
+  if (!policies.Equals(entry->policies)) {
+    // Swap first, so that observers that call GetPolicies() see the current
+    // values.
+    entry->policies.Swap(&policies);
+    // |policies| now contains the previous values, and |entry->policies|
+    // contains the current values.

[Mattias Nissler (ping if slow), 2012/04/23 14:20:44]

I think this comment is redundant and can be removed (it just explains the
behavior of the Swap one line before, which does exactly what it's expected to
do).

[Joao da Silva, 2012/04/23 14:53:19]

Done.

+    FOR_EACH_OBSERVER(
+        PolicyService::Observer,
+        entry->observers,
+        OnPolicyUpdated(POLICY_DOMAIN_CHROME, "", policies, entry->policies));
   }
 
   // Check if all providers became initialized just now, if they weren't before.
   if (!initialization_complete_) {
     initialization_complete_ = true;
     for (ProviderList::iterator iter = providers_.begin();
          iter != providers_.end(); ++iter) {
       if (!(*iter)->provider->IsInitializationComplete()) {
         initialization_complete_ = false;
         break;
       }
     }
     if (initialization_complete_) {
       for (EntryMap::iterator i = entries_.begin(); i != entries_.end(); ++i) {
         FOR_EACH_OBSERVER(PolicyService::Observer,
                           i->second->observers,
                           OnPolicyServiceInitialized());
       }
     }
   }
 }
 
 }  // namespace policy