Use proper pair type in range-based for map iterations.

Since map<Key, Value>::value_type is std::pair<const Key, Value>, we
need to ensure that we use this type to avoid an extra copy/temporary
creation. This patch does this by explicitly using value_type where
it is clear what the type is, and adding const to the key where it's not.

Review URL: https://codereview.chromium.org/853533002

Cr-Commit-Position: refs/heads/master@{#311524}

chrome/browser/history/expire_history_backend_unittest.cc

@@ -333,7 +333,7 @@ void ExpireHistoryTest::EnsureURLInfoGone(const URLRow& row, bool expired) {
   // EXPECT_FALSE(HasThumbnail(row.id()));
 
   bool found_delete_notification = false;
-  for (const std::pair<bool, URLRows>& pair : urls_deleted_notifications_) {
+  for (const auto& pair : urls_deleted_notifications_) {
     EXPECT_EQ(expired, pair.first);
     const history::URLRows& rows(pair.second);
     history::URLRows::const_iterator it_row = std::find_if(

chrome/browser/supervised_user/supervised_user_url_filter.cc

@@ -315,7 +315,7 @@ SupervisedUserURLFilter::GetFilteringBehaviorForURL(
 
   // Look for patterns matching the hostname, with a value that is different
   // from the default (a value of true in the map meaning allowed).
-  for (const std::pair<std::string, bool>& host_entry : host_map_) {
+  for (const auto& host_entry : host_map_) {
     if ((host_entry.second == (default_behavior_ == BLOCK)) &&
         HostMatchesPattern(host, host_entry.first)) {
       return host_entry.second ? ALLOW : BLOCK;

extensions/browser/api/hid/hid_device_manager.cc

@@ -236,7 +236,7 @@ scoped_ptr<base::ListValue> HidDeviceManager::CreateApiDeviceList(
   DCHECK(hid_service);
 
   scoped_ptr<base::ListValue> api_devices(new base::ListValue());
-  for (const std::pair<int, HidDeviceId>& map_entry : device_ids_) {
+  for (const ResourceIdToDeviceIdMap::value_type& map_entry : device_ids_) {
     int resource_id = map_entry.first;
     const HidDeviceId& device_id = map_entry.second;
 

net/quic/quic_stream_factory.cc

@@ -1146,7 +1146,7 @@ void QuicStreamFactory::InitializeCachedStateInCryptoConfig(
 
   if (http_server_properties_) {
     if (quic_supported_servers_at_startup_.empty()) {
-      for (const std::pair<net::HostPortPair, net::AlternateProtocolInfo>&
+      for (const std::pair<const net::HostPortPair, net::AlternateProtocolInfo>&
                key_value : http_server_properties_->alternate_protocol_map()) {
         if (key_value.second.protocol == QUIC) {
           quic_supported_servers_at_startup_.insert(key_value.first);