Don't reset quality scaler on resolution change.
Don't reset quality scaler on resolution change.

This was causing the QualityScaler to be reconstructed each time
the resolution changes and thus the fast_rampup logic was not working
as intended. We now properly change the checking period to 5 seconds
after a downscale.

BUG=b/36457883

Review-Url: https://codereview.webrtc.org/2766513003
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#17335}

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