[Reland #1] macOS: Display [ctr + tab] and [ctr + shift + tab] as hotkeys for tab switching.

The first CL caused test failures because the browser_test was ignoring the
"shift" key when searching for menu items. The IDC_SELECT_NEXT_TAB and
IDC_SELECT_PREVIOUS_TAB only differ by the presence of "shift", so it cannot be
ignored.

> This matches other macOS application like Safari, Terminal, etc. All existing
> hotkeys will still work.
>
> This CL uses the same hotkey for "previous tab" that Safari and Terminal use,
> which is [ctr + shift + "Horizontal Tab"]. This also causes tests to pass.
> However, pressing that key combination actually generates [ctr + shift + "End of
> Medium"], which renderers in the Main Menu as a backwards tab. This CL updates
> NSMenuItem(ChromeAdditions) to check for this special case.
>
> This CL removes two incorrect DCHECKs from render_widget_host_view_cocoa.mm. I
> regularly hit both of them when running Chromium on a local build. They both
> rely on the false assumption that keyEquivalents in the main menu must have the
> command modifier.
>
> Bug: 851714
> Reviewed-on: https://chromium-review.googlesource.com/1106659
> Commit-Queue: Erik Chen <erikchen@chromium.org>
> Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#574211}

Change-Id: Id87f364f5c5b303e8b9668e79f813a1c23376c98
TBR: avi@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/1134203
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574628}
8 files changed