[DO NOT MERGE] Fix edge swipe logic.

1) Only start delegating upon first move event, if all three fingers went down on the bottom edge.
2) The previous logic only required one finger to be in the edge boundary. It now requires all fingers to be in the edge boundary.
Bug: 162521649
Test: manual

Change-Id: I829c463c63b384642d129ff3b5ccdb0db816ddcd