It looks like this is causing history navigation instead. Observing this on 3456 views and cocoa.

The implementation of [NSApplication sendEvent:] first calls:
  (1) [NSApplication _handleKeyEquivalent:], which calls routeKeyEquivalent().
If that returns NO, then it calls:
  (2) [NSWindow sendEvent:] (this method returns void, as it's the last consumer of NSEvents)
    * This goes through typical responder chain logic. On views, when omnibox is selected, this routes to [BridgedContentView keyDown:].

The reason this bug exists is that (cmd + left arrow) gets processed by (1) before (2) has a chance to see it. There's no clean way to fix this since [NSWindow sendEvent:] returns void, which means we can't route there first and then see if the event is handled. We could theoretically rewrite all our sendEvent: overrides to return a BOOL, but that would be a very large amount of work.

Instead, the easiest way to fix this is to only allow (cmd + left arrow) when the firstResponder is a web contents, and the web contents has chosen not to process the event.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4c9d08451ef94d31e97f189343914cf5144ae5c4

commit 4c9d08451ef94d31e97f189343914cf5144ae5c4
Author: erikchen <erikchen@chromium.org>
Date: Thu Jun 14 17:04:08 2018

macOS: Fix [cmd + left arrow] not working in Omnibox.

After a recent refactor, [cmd + left arrow] would perform history navigation
instead of moving the cursor to the beginning of the Omnibox. This happens
because the processing for the hotkey [triggering history navigation] has higher
priority than the typical event handling flow.

The hotkeys [cmd + left arrow] and [cmd + right arrow] are special, and should
only trigger if the firstResponder is a WebContents, and the WebContents has
chosen not to process the event.

This CL removes handleExtraKeyboardShortcut:, which was dead code.

Bug:  852332 
Change-Id: Id03f5e22337a79d9ca4abfd20d995a8cf8976b2a
Reviewed-on: https://chromium-review.googlesource.com/1099648
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567315}
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/global_keyboard_shortcuts_mac.h
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/global_keyboard_shortcuts_mac.mm
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/global_keyboard_shortcuts_mac_browsertest.mm
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/ui/cocoa/browser_window_cocoa.mm
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/ui/cocoa/chrome_command_dispatcher_delegate.h
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/ui/cocoa/chrome_command_dispatcher_delegate.mm
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/ui/cocoa/chrome_event_processing_window.h
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/ui/cocoa/chrome_event_processing_window.mm
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/chrome/browser/ui/views/frame/browser_frame_mac.mm
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/ui/base/cocoa/command_dispatcher.h
[modify] https://crrev.com/4c9d08451ef94d31e97f189343914cf5144ae5c4/ui/base/cocoa/command_dispatcher.mm