CopyOnWriteBuffer::SetSize to smaller size memcpy less.
CopyOnWriteBuffer::SetSize to smaller size memcpy less.

R=kwiberg@webrtc.org

Review URL: https://codereview.webrtc.org/2317283004 .

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#14166}

ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc