Add missing 'explicit' specifier to GainControlImpl
Add missing 'explicit' specifier to GainControlImpl

Bug: None
Change-Id: I36049e54e61f15e7fed522f625f97bbfae71aed1
Reviewed-on: https://webrtc-review.googlesource.com/c/122460
Reviewed-by: Alessio Bazzica <eed802d553432598d8dd1392efc4d65b5eefde4d@webrtc.org>
Commit-Queue: Sam Zackrisson <b1a93beadfe1d2f7f0106ee02b6ffcdc950aa103@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#26645}
ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc