I am a Linux user when using a desktop but OS X for laptops. My need is to insure that I have the same shortcut for the Inspector using Chrome. It was very inconvenient to have the Mail.app popup each time that I would confuse the shortcuts.
I should add that in order to make Linux closer to OSX I swap the control and the alt keys on the Linux side. This allows me to use Ctrl-c, Ctrl-v and many other shortcuts in the more ergonomic position of the command key, e.g. OS X Cmd-c, Cmd-v. In the pictures you will see that I have mapped Ctrl-Shift-I which would not make sense in the Linux side otherwise.
Here is my shortcuts setup

The important part of the setting is to know that the OSX shortcut must be mapped to the exact name of the menu entry. I stated that I am using High Sierra because "Email Link" is the menu label. This could also be dependent on the Chrome version I suppose. Make sure the spelling is identical.
The steps to reproduce are
- Apple Menu System Preferences ...
- Keyboard Menu
- Shortcuts Tab
- App Shortcuts from the left Pane
- Click the Plus sign under the right pane
- Select YOUR APP from the applications list, in my case Chrome
- Add the name of the menu label, in my case Email Link
- Add some shortcut you will not use, in my case Cmd-Shift-E
- Then, add another shortcut for the target operation, in my case Developer Tools
- Add the desired shortcut, in my case Cmd-Shift-I