Reland my close on idle socket change.

net/socket/client_socket_pool_base.h

Index: net/socket/client_socket_pool_base.h
diff --git a/net/socket/client_socket_pool_base.h b/net/socket/client_socket_pool_base.h
index 55ce7f7094dfa72ebc47e56252fd706a4b23e81d..23b293b76bcdcd21535c11ec9730b4ec6e561a93 100644
--- a/net/socket/client_socket_pool_base.h
+++ b/net/socket/client_socket_pool_base.h
@@ -225,7 +225,7 @@ class ClientSocketPoolBaseHelper
     return connect_job_factory_->ConnectionTimeout();
   }
 
-  void enable_backup_jobs() { backup_jobs_enabled_ = true; };
+  void EnableBackupJobs() { backup_jobs_enabled_ = true; };
 
  private:
   friend class base::RefCounted<ClientSocketPoolBaseHelper>;
@@ -387,6 +387,13 @@ class ClientSocketPoolBaseHelper
   // Called when the backup socket timer fires.
   void OnBackupSocketTimerFired(const std::string& group_name);
 
+  // Closes one idle socket.  Picks the first one encountered.
+  // TODO(willchan): Consider a better algorithm for doing this.  Perhaps we
+  // should keep an ordered list of idle sockets, and close them in order.
+  // Requires maintaining more state.  It's not clear if it's worth it since
+  // I'm not sure if we hit this situation often.
+  void CloseOneIdleSocket();
+
   GroupMap group_map_;
 
   // Timer used to periodically prune idle sockets that timed out or can't be
@@ -426,9 +433,13 @@ class ClientSocketPoolBaseHelper
   // |max_sockets_per_group_| limit. So choosing the next request involves
   // selecting the highest priority request across *all* groups.
   //
-  // Since reaching the maximum number of sockets is an edge case, we make note
-  // of when it happens, and thus avoid doing the slower "scan all groups"
-  // in the common case.
+  // |may_have_stalled_group_| is not conclusive, since when we cancel pending
+  // requests, we may reach the situation where we have the maximum number of 
+  // sockets, but not request is stalled because of the global socket limit
+  // (although some requests may be blocked on the socket per group limit).
+  // We don't strictly maintain |may_have_stalled_group_|, since that would
+  // require a linear search through all groups in |group_map_| to see if one 
+  // of them is stalled.
   bool may_have_stalled_group_;
 
   const scoped_ptr<ConnectJobFactory> connect_job_factory_;
@@ -568,7 +579,7 @@ class ClientSocketPoolBase {
 
   const std::string& name() const { return name_; }
 
-  void enable_backup_jobs() { helper_->enable_backup_jobs(); };
+  void EnableBackupJobs() { helper_->EnableBackupJobs(); };
 
  private:
   // This adaptor class exists to bridge the