Takumi could you take a look at this for M57?  Derek said he could help you with the policy pieces here.

Extensions installed by an administrator has an "Installed by your
administrator" menu item with a little administrator icon, instead of "Remove
from Chrome." Should we also replace "Always show icon" with something like
"Added by your administrator" with an icon?

Yes, that would make sense.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1

commit 1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1
Author: takumif <takumif@chromium.org>
Date: Tue Jan 31 19:10:50 2017

Add a policy to always show the Cast toolbar icon

This CL adds a policy "ShowCastIconInToolbar," which will force the media router
toolbar action to be always shown in the toolbar or the overflow menu when
enabled.

When the policy is enabled, the action's context menu item "Always show icon"
will be replaced by "Added by your administrator," similar to the item
"Installed by your administrator" for policy-enabled extensions. This menu item
will always be disabled.

This CL adds a new pref with ID prefs::kShowCastIconInToolbar for the policy.
When we later remove ComponentMigrationHelper and the prefs associated with it
that we currently use to pin the media router action to the toolbar, we can use
prefs::kShowCastIconInToolbar to record user-initiated pinning of the action to
the toolbar.

BUG= 666003 

Review-Url: https://codereview.chromium.org/2559323002
Cr-Commit-Position: refs/heads/master@{#447289}

[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/app/chrome_command_ids.h
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/app/media_router_strings.grdp
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/policy/configuration_policy_handler_list_factory.cc
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/policy/policy_browsertest.cc
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/profiles/profile_impl.cc
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/ui/toolbar/component_toolbar_actions_factory.cc
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/ui/toolbar/media_router_action_controller.cc
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/ui/toolbar/media_router_action_controller.h
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/ui/toolbar/media_router_contextual_menu.cc
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/ui/toolbar/media_router_contextual_menu.h
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/browser/ui/toolbar/media_router_contextual_menu_unittest.cc
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/common/pref_names.cc
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/common/pref_names.h
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/chrome/test/data/policy/policy_test_cases.json
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/components/policy/resources/policy_templates.json
[modify] https://crrev.com/1a5f2851a8a4cf5222a676dc8bcc7d52fc29a7f1/tools/metrics/histograms/histograms.xml