Charging a Li-Ion Battery
Is there any chip that justs stop the flow of current once the battery
  has reached 4.2?


In charging of Li-Ion batteries the chargers do not stop when the voltage is reached 4.2 V (or 4.35 for Li-Po). If the chargers would do so, the battery cell will be charged to maybe 50% of its rated capacity. In fact, the charger voltage is slowly creeping up around 4.2 V for a while when the cell accumulates energy sucking full charge current (CC stage). The charger continues to keep 4.2V until the charge current starts dropping due to internal cell approaching full charge, and [charger] stops [voltage supply] when the current usually reaches 1/10 of main charging current (cut-off current). Because of this very slow slope in voltage the criteria of reaching 4.2V will be very unreliable, and is not used.

Technically every good programmable charger can set the cut-off threshold to much higher level. For example, the BQ2xxxx family of chargers from Texas Instruments can set the termination current limit to a wide range of values.