Closure compile: add missing ui BUILD.gn extern dependencies

 - banners.js depends on type {chrome.echoPrivate}
   - add externs deps: externs/chrome_echo_private.js
 - combobutton.js and files_menu.js depend on type {PaperRipple}
   - add externs deps: externs/paper_elements.js
 - providers_menu.js depends on type {MenuItemUpdateEvent}
   - add externs deps: externs/menu_item_update_event.js
 - search_box.js depends on type {SearchItem}
   - add externs deps: externs/search_item.js
 - suggest_apps_dialog.js depends on {chrome.webstoreWidgetPrivate}
   - add externs deps: externs/chrome_webstore_widget_private.js

No change in test behavior, no new tests.

Bug: 910975
Change-Id: Ib38947f6f6717b9767be6ec4472b1bbd16ac384a
Reviewed-on: https://chromium-review.googlesource.com/c/1356734Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612988}

ui/file_manager/file_manager/foreground/js/ui/BUILD.gn

@@ -101,6 +101,7 @@ js_library("banners") {
     "//ui/webui/resources/js:assert",
     "//ui/webui/resources/js/cr:event_target",
   ]
+  externs_list = [ "../../../../externs/chrome_echo_private.js" ]
 }
 
 js_library("combobutton") {
@@ -109,6 +110,7 @@ js_library("combobutton") {
     "../../elements:files_toggle_ripple",
     "//ui/webui/resources/js/cr/ui:menu_button",
   ]
+  externs_list = [ "../../../../externs/paper_elements.js" ]
 }
 
 js_library("commandbutton") {
@@ -321,6 +323,7 @@ js_library("files_menu") {
     "//ui/webui/resources/js/cr/ui:menu",
     "//ui/webui/resources/js/cr/ui:menu_item",
   ]
+  externs_list = [ "../../../../externs/paper_elements.js" ]
 }
 
 js_library("install_linux_package_dialog") {
@@ -378,6 +381,7 @@ js_library("providers_menu") {
     "//ui/webui/resources/js/cr/ui:menu",
     "//ui/webui/resources/js/cr/ui:position_util",
   ]
+  externs_list = [ "../../../../externs/menu_item_update_event.js" ]
 }
 
 js_library("search_box") {
@@ -392,6 +396,7 @@ js_library("search_box") {
     "//ui/webui/resources/js/cr:ui",
     "//ui/webui/resources/js/cr/ui:autocomplete_list",
   ]
+  externs_list = [ "../../../../externs/search_item.js" ]
 }
 
 js_library("suggest_apps_dialog") {
@@ -406,6 +411,7 @@ js_library("suggest_apps_dialog") {
     "../../../cws_widget:cws_widget_container",
     "//ui/file_manager/base/js:volume_manager_types",
   ]
+  externs_list = [ "../../../../externs/chrome_webstore_widget_private.js" ]
 }
 
 js_unit_tests("unit_tests") {