chrome: Support configuration of Chrome policy management (fixes #3581)

Disable Chrome policy management by default. Add CefSettings.chrome_policy_id
which, when configured, enables Chrome policy management. See
https://support.google.com/chrome/a/answer/9037717 for background.

To test:
- Start with a machine where Google Chrome is managed.
- Run `cefclient --enable-chrome-runtime --url=chrome://policy/`
  There should be no configured policies.
- Run `cefclient --enable-chrome-runtime --url=chrome://policy/
       --enable-chrome-policy`
  Configured Platform properties should match Google Chrome.
- Run `cefclient --enable-chrome-runtime --url=chrome://policy/
       --enable-chrome-policy --enable-chrome-browser-cloud-management`
  Configured Platform and Cloud properties should match Google Chrome.

tests/cefclient/browser/main_context_impl.cc

@@ -214,6 +214,23 @@ void MainContextImpl::PopulateSettings(CefSettings* settings) {
     CefString(&settings->accept_language_list) =
         command_line_->GetSwitchValue("lang");
   }
+
+  if (command_line_->HasSwitch("enable-chrome-policy")) {
+    // Enable Chrome policy management via Platform and OS-user policies.
+    // Use the same configuration ID as Google Chrome for testing purposes.
+    // If Google Chrome is managed on this machine we'll show the same
+    // configured policies in chrome://policy/.
+    CefString(&settings->chrome_policy_id) =
+#if defined(OS_WIN)
+        "SOFTWARE\\Policies\\Google\\Chrome";
+#elif defined(OS_MAC)
+        "com.google.Chrome";
+#elif defined(OS_LINUX)
+        "/etc/opt/chrome/policies";
+#else
+        "";
+#endif
+  }
 }
 
 void MainContextImpl::PopulateBrowserSettings(CefBrowserSettings* settings) {