Git Diff Flex adds a draggable pane bezel between two files when comparing diffs! Currently only for github.com.
https://chrome.google.com/webstore/detail/git-diff-flex/deholaolbodagbifbcaghhmjlbekndec
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.