Function declaration

Execution flow

1. Checks whether a sequence of input events is self-consistent.

2. Filter the touch event to apply security policies.

3. Handle an initial down.

4. Check for interception.

5. Check for cancelation.

6. Distribute the ACTION_DOWN eventTODO 部分，具体过程如下：（参考 ViewGroup dispatchTouchEvent）

1. Dispatch to touch targets.

2. Update list of touch targets for pointer up or cancel, if needed.

3. If the event still was not intercepted. Then, notifies the verifier that a given event was unhandled and the rest of the trace for the event should be ignored.