Thanks for the report.  Right, we should be suppressing a jump when the cursor is visible and in the prompt.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/60c81ca7fbd73c42c303d4ce65730f802575636c

commit 60c81ca7fbd73c42c303d4ce65730f802575636c
Author: Erik Luo <luoe@chromium.org>
Date: Thu Feb 08 23:58:39 2018

DevTools: do not scroll console to bottom when prompt cursor is visible

When messages are visible, the prompt is multiline, and viewport is
not scrolled to the bottom, typing used to jump to the bottom. After
this CL, it will not.

This is better since users can type without jumping. The downside is
that, when the cursor is not at the last line of the prompt and a
flood of new messages arrive, the incoming messages can push the
prompt out of view. While not 100% ideal, users can keep the prompt
position fixed by manually dragging the scrollbar to the bottom.

Bug:  646056 
Change-Id: I2e36000510f853f4b3316db79dce6619e0923133
Reviewed-on: https://chromium-review.googlesource.com/830617
Commit-Queue: Erik Luo <luoe@chromium.org>
Reviewed-by: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#535579}
[modify] https://crrev.com/60c81ca7fbd73c42c303d4ce65730f802575636c/third_party/WebKit/LayoutTests/http/tests/devtools/console/console-viewport-stick-to-bottom-expected.txt
[modify] https://crrev.com/60c81ca7fbd73c42c303d4ce65730f802575636c/third_party/WebKit/LayoutTests/http/tests/devtools/console/console-viewport-stick-to-bottom.js
[modify] https://crrev.com/60c81ca7fbd73c42c303d4ce65730f802575636c/third_party/WebKit/Source/devtools/front_end/console/ConsoleView.js