[TaskManager] Check iterators' availability before manipulating them.

There are some DCHECK() to check iterators, but it checks
nothing in release builds.
We have to check them to avoid crashes in release builds.


BUG=364243

Review URL: https://codereview.chromium.org/338993004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@277963 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/task_manager/task_manager.cc

@@ -994,6 +994,8 @@ void TaskManagerModel::RemoveResource(Resource* resource) {
   // Find the associated group.
   GroupMap::iterator group_iter = group_map_.find(process);
   DCHECK(group_iter != group_map_.end());
+  if (group_iter == group_map_.end())
+    return;
   ResourceList& group_entries = group_iter->second;
 
   // Remove the entry from the group map.
@@ -1001,7 +1003,8 @@ void TaskManagerModel::RemoveResource(Resource* resource) {
                                           group_entries.end(),
                                           resource);
   DCHECK(iter != group_entries.end());
-  group_entries.erase(iter);
+  if (iter != group_entries.end())
+    group_entries.erase(iter);
 
   // If there are no more entries for that process, do the clean-up.
   if (group_entries.empty()) {
@@ -1016,27 +1019,26 @@ void TaskManagerModel::RemoveResource(Resource* resource) {
     }
   }
 
-  // Prepare to remove the entry from the model list.
+  // Remove the entry from the model list.
   iter = std::find(resources_.begin(), resources_.end(), resource);
   DCHECK(iter != resources_.end());
-  int index = static_cast<int>(iter - resources_.begin());
-
-  // Notify the observers that the contents will change.
-  FOR_EACH_OBSERVER(TaskManagerModelObserver, observer_list_,
-                    OnItemsToBeRemoved(index, 1));
-
-  // Now actually remove the entry from the model list.
-  resources_.erase(iter);
+  if (iter != resources_.end()) {
+    int index = static_cast<int>(iter - resources_.begin());
+    // Notify the observers that the contents will change.
+    FOR_EACH_OBSERVER(TaskManagerModelObserver, observer_list_,
+                      OnItemsToBeRemoved(index, 1));
+    // Now actually remove the entry from the model list.
+    resources_.erase(iter);
+    // Notify the table that the contents have changed.
+    FOR_EACH_OBSERVER(TaskManagerModelObserver, observer_list_,
+                      OnItemsRemoved(index, 1));
+  }
 
   // Remove the entry from the network maps.
   ResourceValueMap::iterator net_iter =
       current_byte_count_map_.find(resource);
   if (net_iter != current_byte_count_map_.end())
     current_byte_count_map_.erase(net_iter);
-
-  // Notify the table that the contents have changed.
-  FOR_EACH_OBSERVER(TaskManagerModelObserver, observer_list_,
-                    OnItemsRemoved(index, 1));
 }
 
 void TaskManagerModel::StartUpdating() {