Does this involve secondary UI dialogs?

Yes it does. I hadn't noticed that. I'm going to mark it as available unless you want to take it.

Weird, there should've been a bug already assigned to me that involves implementing hover support for the secondary UI dialogs, but I can't find it. I'll just use this one.

Anyway, there's currently a lot of issues with omnibox decorations and secondary UI dialogs because we didn't implement any support for it. The decorations rely on the bubbles notifying them the state of the dialog.

 Issue 715861  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/358c00f72ae3bcf3911da69b48403116dc267712

commit 358c00f72ae3bcf3911da69b48403116dc267712
Author: spqchan <spqchan@chromium.org>
Date: Tue May 23 17:40:11 2017

[Mac] Hover/Active Omnibox Icon States for Secondary UI MD

When a secondary UI dialog is opened, the omnibox icon it's anchored to
need to set its state as active. When the dialog is dismissed, the icon is
set to inactive.

BubbleAnchorHelper provides functions to retrieve the omnibox icons
and sets the active state.

BUG= 715863 

Review-Url: https://codereview.chromium.org/2882533003
Cr-Commit-Position: refs/heads/master@{#473963}

[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/BUILD.gn
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/browser_dialogs.h
[rename] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/cocoa/browser_dialogs_views_mac.cc
[add] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/cocoa/browser_dialogs_views_mac.h
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/cocoa/browser_window_controller.mm
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/cocoa/bubble_anchor_helper_views.h
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/cocoa/bubble_anchor_helper_views.mm
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/cocoa/location_bar/content_setting_decoration.mm
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/cocoa/page_info/page_info_bubble_controller.mm
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/cocoa/tab_dialogs_views_mac.mm
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/views/page_info/page_info_bubble_view.cc
[modify] https://crrev.com/358c00f72ae3bcf3911da69b48403116dc267712/chrome/browser/ui/views/page_info/page_info_bubble_view.h

Just need it for zoom. I created a separate issue for that:  Issue 725566