update:

tried to pass just one subscriber.

 // Listen for motor control response
 Subscriber<JointControllerState> j1_sub(n, "/rrbot/joint1_position_controller/state", 10);
// Subscriber<JointControllerState> j2_sub(n, "/rrbot/joint2_position_controller/state", 10);
 typedef sync_policies::ApproximateTime<JointControllerState, JointControllerState> MySyncPolicy;
 Synchronizer<MySyncPolicy> sync(MySyncPolicy(1000), j1_sub);
 sync.registerCallback(boost::bind(&PublishOdometry::handelerOdometry, this, _1));
 ROS_INFO("handelerInitialPose finished processing");

get compilation error:

 Building CXX object gazebo_ros_demos/rrbot_control/CMakeFiles/robot_odometry.dir/src/robot_odometry.cpp.o
/home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp: In member function ‘void PublishOdometry::handelerInitialPose(geometry_msgs::PoseWithCovarianceStampedConstPtr)’:
/home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:163:64: error: no matching function for call to ‘message_filters::Synchronizer<message_filters::sync_policies::ApproximateTime<control_msgs::JointControllerState_<std::allocator<void> >, control_msgs::JointControllerState_<std::allocator<void> > > >::Synchronizer(MySyncPolicy, message_filters::Subscriber<control_msgs::JointControllerState_<std::allocator<void> > >&)’
/home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:163:64: note: candidates are:
In file included from /opt/ros/hydro/include/message_filters/time_synchronizer.h:38:0,
                 from /home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:14:
/opt/ros/hydro/include/message_filters/synchronizer.h:220:3: note: message_filters::Synchronizer<Policy>::Synchronizer(const Policy&) [with Policy = message_filters::sync_policies::ApproximateTime<control_msgs::JointControllerState_<std::allocator<void> >, control_msgs::JointControllerState_<std::allocator<void> > >]
/opt/ros/hydro/include/message_filters/synchronizer.h:220:3: note:   candidate expects 1 argument, 2 provided
/opt/ros/hydro/include/message_filters/synchronizer.h:213:3: note: template<class F0, class F1, class F2, class F3, class F4, class F5, class F6, class F7, class F8> message_filters::Synchronizer::Synchronizer(const Policy&, F0&, F1&, F2&, F3&, F4&, F5&, F6&, F7&, F8&)
/opt/ros/hydro/include/message_filters/synchronizer.h:213:3: note:   template argument deduction/substitution failed:
/home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:163:64: note:   candidate expects 10 arguments, 2 provided
In file included from /opt/ros/hydro/include/message_filters/time_synchronizer.h:38:0,
                 from /home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:14:
/opt/ros/hydro/include/message_filters/synchronizer.h:205:3: note: template<class F0, class F1, class F2, class F3, class F4, class F5, class F6, class F7> message_filters::Synchronizer::Synchronizer(const Policy&, F0&, F1&, F2&, F3&, F4&, F5&, F6&, F7&)
/opt/ros/hydro/include/message_filters/synchronizer.h:205:3: note:   template argument deduction/substitution failed:
/home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:163:64: note:   candidate expects 9 arguments, 2 provided
In file included from /opt/ros/hydro/include/message_filters/time_synchronizer.h:38:0,
                 from /home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:14:
/opt/ros/hydro/include/message_filters/synchronizer.h:197:3: note: template<class F0, class F1, class F2, class F3, class F4, class F5, class F6> message_filters::Synchronizer::Synchronizer(const Policy&, F0&, F1&, F2&, F3&, F4&, F5&, F6&)
/opt/ros/hydro/include/message_filters/synchronizer.h:197:3: note:   template argument deduction/substitution failed:
/home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:163:64: note:   candidate expects 8 arguments, 2 provided
In file included from /opt/ros/hydro/include/message_filters/time_synchronizer.h:38:0,
                 from /home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:14:
/opt/ros/hydro/include/message_filters/synchronizer.h:189:3: note: template<class F0, class F1, class F2, class F3, class F4, class F5> message_filters::Synchronizer::Synchronizer(const Policy&, F0&, F1&, F2&, F3&, F4&, F5&)
/opt/ros/hydro/include/message_filters/synchronizer.h:189:3: note:   template argument deduction/substitution failed:
/home/viki/catkin_ws/src/gazebo_ros_demos/rrbot_control/src/robot_odometry.cpp:163:64: note:   candidate expects 7 arguments, 2 provided
In file included from /opt/ros/hydro/include/message_filters/time_synchronizer.h:38:0,

Update: I modified the MyPolicy to 1000. Here is a rostopic echo for /rrbot/joint1positioncontroller/state and /rrbot/joint2positioncontroller/state. They are published with identical time stamps.

rostopic echo /rrbot/joint1_position_controller/state
header: 
  seq: 121
  stamp: 
    secs: 12
    nsecs: 742000000
  frame_id: ''
set_point: 0.0
process_value: -0.0157292577876
process_value_dot: 0.0
error: 0.0157292577876
time_step: 0.01
command: 0.707721581498
p: 45.0
i: 0.2
d: 0.1
i_clamp: 0.0

rostopic echo /rrbot/joint2_position_controller/state

header: 
  seq: 121
  stamp: 
    secs: 12
    nsecs: 742000000
  frame_id: ''
set_point: 0.0
process_value: -0.00342763697945
process_value_dot: 0.0
error: 0.00342763697945
time_step: 0.01
command: 0.154095246248
p: 45.0
i: 0.2
d: 0.1
i_clamp: 0.0

The callback is never called. The ROS_INFO print line does print so this code is executed. The topics are published by gazebo via the gazebo-ros plugin for the two joints. So why is the callback not called?

  // Listen for motor control response
     Subscriber<JointControllerState> j1_sub(n, "/rrbot/joint1_position_controller/state", 10);
     Subscriber<JointControllerState> j2_sub(n, "/rrbot/joint2_position_controller/state", 10);
     typedef sync_policies::ApproximateTime<JointControllerState, JointControllerState> MySyncPolicy;
     Synchronizer<MySyncPolicy> sync(MySyncPolicy(10), j1_sub, j2_sub);
     sync.registerCallback(boost::bind(&PublishOdometry::handelerOdometry, this, _1, _2));
     ROS_INFO("handelerInitialPose finished processing");