Layout:Resizable Panes

Build 2871 on feat-improved-styles
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Baseline History
Build 28718f369bf
Current build. There are unaccepted changes, so build 2752 is still the baseline.
Build 275208ed3c8 current baseline
Accepted by Andrey Yamanov.
Build 258343caac6
Auto-accepted
Commenting is disabled because there's a newer build on this branch