UserAgent: Mozilla/5.0 (X11; CrOS x86_64 10032.86.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.140 Safari/537.36
Platform: 10032.86.0 (Official Build) stable-channel eve

Steps to reproduce the problem:
There are several setups that can be used in order to reproduce the problem:

SETUP 1:
0. Download the Secure Shell app in a Chromium OS environment if it is not already installed: https://chrome.google.com/webstore/detail/secure-shell/pnhechapfaindjhompbnflcldabbghjo
1. Open the Secure Shell app
2. Log in via SSH to an Ubuntu computer in the network.

SETUP 2:
0. Turn on the device's developer mode.
1. Open Crosh via the Ctrl+Shift+T shortcut.
2. Type shell and hit enter.
3. Set up a SSH connection with an Ubuntu computer in the network and SSH to that device.

SETUP 3:
0. Turn on the device's developer mode.
1. Download crouton and create a new Ubuntu Xenial chroot.
2. In the crosh shell, type `sudo enter-chroot` to enter the crouton chroot.

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Now, we can proceed with the steps in order to reproduce the problem:

0. Make sure vim is installed by running the following command:
  which vim
1. If it is not installed, install it by running:
  sudo apt-get update
  sudo apt-get install vim
2. Run the following command to generate a sample text file with several lines.
  for ((i=1;i<=100;i++)); do echo $i > sample.txt; done
3. Open the generated file in vim by using the following command:
  vim sample.txt
4. Press the colon key (:), and type the following after the colon:
  :set mouse=a
5. Try to scroll through the text with the touchpad (by placing two fingers in the touchpad).

What is the expected behavior?
6. Vim should scroll through the file.

What went wrong?
6. Vim is not scrolling. Nevertheless, if you click a character the cursor is moved to that character, so only the scrolling behavior is not working properly.

Also, after trying to scroll, if you click a character Vim doesn't move the cursor to that character, instead you have to click a second time.

Did this work before? Yes I don't remember the exact version, but some weeks ago it worked, so it should work ok in v62.

Chrome version: 63.0.3239.140  Channel: stable
OS Version: 10032.86.0
Flash Version: 

I've tested this with eve and peppy, and am getting the exact same results.