The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8f6d7316365629613e3e9b1635df64e1aedfe21e

commit 8f6d7316365629613e3e9b1635df64e1aedfe21e
Author: Melissa Zhang <melzhang@google.com>
Date: Mon Dec 10 06:25:09 2018

Implement chrome://app-icon to serve app icons to WebUI.

This CL adds an app icon page at
chrome://app-icon/<app-id>/<icon-size> when the feature AppManagement
is enabled.

A request must be made to chrome://apps first to initialise the
URLDataSource from which app icons are retrieved.

This involves:
- Adding AppIconSource
- Initialising URLDataSource in App Management
- Creating the url in webui urls

BUG=912371

Change-Id: Iba29dbd4fff35b60630fd2ec4337e8a94f9bd741
Reviewed-on: https://chromium-review.googlesource.com/c/1361752
Reviewed-by: calamity <calamity@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Melissa Zhang <melzhang@google.com>
Cr-Commit-Position: refs/heads/master@{#615054}
[modify] https://crrev.com/8f6d7316365629613e3e9b1635df64e1aedfe21e/chrome/browser/BUILD.gn
[add] https://crrev.com/8f6d7316365629613e3e9b1635df64e1aedfe21e/chrome/browser/apps/app_service/app_icon_source.cc
[add] https://crrev.com/8f6d7316365629613e3e9b1635df64e1aedfe21e/chrome/browser/apps/app_service/app_icon_source.h
[modify] https://crrev.com/8f6d7316365629613e3e9b1635df64e1aedfe21e/chrome/browser/ui/webui/app_management/app_management_ui.cc
[modify] https://crrev.com/8f6d7316365629613e3e9b1635df64e1aedfe21e/chrome/common/webui_url_constants.cc
[modify] https://crrev.com/8f6d7316365629613e3e9b1635df64e1aedfe21e/chrome/common/webui_url_constants.h