[Extensions Click-to-Script] Add help article in chrome://extensions

Add a link to the help article for runtime host permissions in
the chrome://extensions page.

Note: the article that lives at this page is currently a placeholder,
and will be updated on the server.

Bug: 877664

Change-Id: Idc46b063d502b99458457679f279fa8d10e8e131
Reviewed-on: https://chromium-review.googlesource.com/1220473Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591530}

chrome/app/md_extensions_strings.grdp

@@ -91,6 +91,9 @@
   <message name="IDS_MD_EXTENSIONS_HOST_PERMISSIONS_EDIT" desc="The label of the button used to edit an extension's access to a given website.">
     Edit
   </message>
+  <message name="IDS_MD_EXTENSIONS_HOST_PERMISSIONS_LEARN_MORE" desc="The caption containing the link at which the user can learn more about extension host access">
+    Learn more about <ph name="BEGIN_LINK">&lt;a target="_blank" href="$1"&gt;</ph>site access<ph name="END_LINK">&lt;/a&gt;</ph>
+  </message>
   <message name="IDS_MD_EXTENSIONS_ITEM_ERRORS" desc="The label of the button to bring the user to the page showing an extension's errors.">
     Errors
   </message>

chrome/browser/extensions/BUILD.gn

@@ -472,6 +472,8 @@ jumbo_static_library("extensions") {
     "chrome_content_verifier_delegate.h",
     "chrome_extension_api_frame_id_map_helper.cc",
     "chrome_extension_api_frame_id_map_helper.h",
+    "chrome_extension_browser_constants.cc",
+    "chrome_extension_browser_constants.h",
     "chrome_extension_chooser_dialog.h",
     "chrome_extension_function.cc",
     "chrome_extension_function.h",

chrome/browser/extensions/chrome_extension_browser_constants.cc

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/extensions/chrome_extension_browser_constants.h"
+
+namespace chrome_extension_constants {
+
+// The link to the help article for runtime host permissions.
+const char kRuntimeHostPermissionsHelpURL[] =
+    "https://support.google.com/chrome?p=enable_extensions";
+
+}  // namespace chrome_extension_constants

chrome/browser/extensions/chrome_extension_browser_constants.h

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_BROWSER_CONSTANTS_H_
+#define CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_BROWSER_CONSTANTS_H_
+
+// Constants that are only needed by the //chrome/browser layer, and thus
+// don't need to be in //extensions/common.
+namespace chrome_extension_constants {
+
+extern const char kRuntimeHostPermissionsHelpURL[];
+
+}  // namespace chrome_extension_constants
+
+#endif  // CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_BROWSER_CONSTANTS_H_

chrome/browser/resources/md_extensions/runtime_host_permissions.html

@@ -37,10 +37,20 @@
         display: flex;
         justify-content: space-between;
       }
+
+      a[href] {
+        color: var(--google-blue-700);
+        text-decoration: none;
+      }
     </style>
     <div id="permissions-mode">
-      <div class="mid-section-header">
-        $i18n{hostPermissionsHeading}
+      <div>
+        <div class="mid-section-header">
+          $i18n{hostPermissionsHeading}
+        </div>
+        <div>
+          $i18nRaw{hostPermissionsLearnMoreLink}
+        </div>
       </div>
       <select id="host-access" class="md-select"
           value="[[permissions.hostAccess]]"

chrome/browser/ui/webui/extensions/extensions_ui.cc

@@ -13,6 +13,7 @@
 #include "base/timer/elapsed_timer.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
+#include "chrome/browser/extensions/chrome_extension_browser_constants.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/webui/metrics_handler.h"
 #include "chrome/common/pref_names.h"
@@ -30,8 +31,8 @@
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_observer.h"
-#include "content/public/browser/web_ui_data_source.h"
 #include "content/public/browser/web_ui.h"
+#include "content/public/browser/web_ui_data_source.h"
 #include "content/public/common/content_features.h"
 #include "extensions/common/extension_urls.h"
 #include "ui/base/l10n/l10n_util.h"
@@ -307,6 +308,12 @@ content::WebUIDataSource* CreateMdExtensionsSource(bool in_dev_mode) {
               GURL(extension_urls::GetWebstoreExtensionsCategoryURL()),
               g_browser_process->GetApplicationLocale())
               .spec()));
+  source->AddString(
+      "hostPermissionsLearnMoreLink",
+      l10n_util::GetStringFUTF16(
+          IDS_MD_EXTENSIONS_HOST_PERMISSIONS_LEARN_MORE,
+          base::ASCIIToUTF16(
+              chrome_extension_constants::kRuntimeHostPermissionsHelpURL)));
 
   source->AddBoolean(kInDevModeKey, in_dev_mode);
   source->AddString(kLoadTimeClassesKey, GetLoadTimeClasses(in_dev_mode));