Fixed view source shortcut to be CTRL+U, not CTRL+ALT+U

[mrpapercut]

Test plan

#7704 (comment)

1. Launch Brave on macOS and visit brave.com
2. Verify view source shortcut is unchanged; it should be Cmd + Option + U
3. Launch Brave on Windows (or Linux) and visit brave.com
4. Press Ctrl + U and verify view source comes up as expected

Original issue description

• Did you search for similar issues before submitting this one?
  Yes

• Describe the issue you encountered:
  View Source shortcut should be CTRL+U, not CTRL+ALT+U

• Platform (Win7, 8, 10? macOS? Linux distro?):
  All

• Brave Version (revision SHA):
  1db81cb

• Steps to reproduce:

  1. Go to //brave.com
  2. Press CTRL+U (win) or CMD+U (darwin)

• Actual result:
  Nothing happens

• Expected result:
  URI view-source:https://brave.com is loaded in a new tab
  The context-menu option to View Source indicates that the shortcut should be CTRL+U

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes

• Is this an issue in the currently released version?
  Yes

• Can this issue be consistently reproduced?
  Yes

• Any related issues:
  Referenced in, but not related to Fixed keyboard shortcuts not working #7491. View-Source shortcut still doesn't work even after commit 5a889cc (but that commit is necessary for any keybindings to work)

[NejcZdovc]

Opera and Firefox is using CTRL+U, but Safari and Chrome is using CTRL+ALT+U

cc @bsclifton @bradleyrichter @bbondy Thoughts? I would personally leave as it is

[mrpapercut]

On Windows Chrome it's Ctrl+U
On Mac Chrome it's Cmd+Alt+U
On Safari there is no View Page like in Brave, but Cmd+Alt+U opens the devtools

The contextmenu of Brave says that it's Ctrl+U on windows, and the keymapping was set to Ctrl+Alt+U. Hence my issue and changes

[NejcZdovc]

@mrpapercut Yeah sorry I should wrote it in the comment above that I am testing it on a macOS. What I would suggest is then to edit context menu to represent the correct shortcut.

[mrpapercut]

No problem, I had to check with someone else to figure out the macOS shortcuts too :)

So the difference is really windows/linux vs. macOS, as all browsers (IE & Edge as well) on Win use Ctrl+U and those on Mac use Cmd+Alt+U.

There already is an OS condition in the same file for different keys. My suggestion is that I create a new PR that uses Cmd+Alt+U for darwin and Ctrl+U for win, as that is most widely implemented