UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3530.0 Safari/537.36

Steps to reproduce the problem:
1. Capture a timeline in DevTools/Performance.
2. Focus on a particular area by zooming in (point, then scroll).
3. Investigate its deeper stack by scrolling down (hold shift and scroll)

What is the expected behavior?
It should be as easy with a mouse as with a trackpad.

What went wrong?
Holding down shift and scrolling (with a mouse) results in no visible change on the screen.

Did this work before? N/A 

Chrome version: 70.0.3530.0  Channel: n/a
OS Version: OS X 10.13.6
Flash Version: 

I've only recently started using a mouse (after years of using a trackpad to navigate Chrome DevTools). After some investigating, I found that the underlying issue is that when holding down shift the meaning of the scroll changes from vertical to horizontal.

I noticed this by observing the mousewheel events which were still being fired both with and without the Shift key being held down, except that deltaX was being manipulated, instead of deltaY.

However, while mousewheel events were firing, holding "Shift" resulted in the scroll event not firing anymore.

This means there are arguably three problems:

* People looking to scroll horizontally (left to right) with Shift+scroll (which works in all other regular web and app contexts), are surprised by Shift+scroll doing nothing.

* People looking to conveniently change between zoom and pan (like trackpad users would, by only pressing and depressing Shift), are surprised by Shift+scroll doing nothing. I was ready to sacrifice the ability to scroll horizontally, except there is no way in either the Logitech driver, nor macOS, nor Chrome, to restore "shift+scroll" from doing what it would with a trackpad, which is to fire a shift key while normally scrolling. Instead, all three insist on horizontal scrolling.

Given this was making it impossible to scroll down at all, I eventually found a workaround thanks to  issue 725156 , which is to change the  "Flamechart mouse wheel action" setting in DevTools from "Zoom" (default) to "Scroll".

However, this leaves me with two problems:

* I still can't conveniently zoom and pan. I can now pan, but to zoom one has to move mental focus away from flamechart, to the horizontal slider on top, scroll to zoom there, and then move focus back. It should be as easy with a mouse as with a trackpad.

* I now also lose this ability when using a trackpad because the setting can only have one value.

### Proposal

I believe the simplest solution would be for DevTools to either:

1. Support activating/deactivating of Timeline Pan mode with a key other than Shift.

2. Automatically perform Timeline Pan when shift is held and horizontal mousewheel events are received. Right now, when holding shift and scrolling, nothing happens (not even a horizontal scroll), so it seems that this user action is currently unused and could be put to use in this way without conflict.