Remove explicit marker from ProcessMap.

chrome/browser/extensions/process_map.cc

 // Copyright (c) 2011 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/extensions/process_map.h"
 
 namespace extensions {
 
 // Item
 struct ProcessMap::Item {
   Item() {
   }
 
-  explicit Item(const ProcessMap::Item& other)
+  // Purposely implicit constructor needed on older gcc's. See:
+  // http://codereview.chromium.org/8769022/
+  Item(const ProcessMap::Item& other)
       : extension_id(other.extension_id),
         process_id(other.process_id),
         site_instance_id(other.site_instance_id) {
   }
 
   Item(const std::string& extension_id, int process_id,
        int site_instance_id)
       : extension_id(extension_id),
         process_id(process_id),
         site_instance_id(site_instance_id) {
@@ skipping 79 matching lines @@
   std::set<std::string> result;
   for (ItemSet::const_iterator iter = items_.begin(); iter != items_.end();
        ++iter) {
     if (iter->process_id == process_id)
       result.insert(iter->extension_id);
   }
   return result;
 }
 
 }  // extensions