Add observers for DIP scale change.

components/external_video_surface/BUILD.gn

 # Copyright 2015 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.
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 source_set("external_video_surface") {
   if (is_android) {
@@ skipping 12 matching lines @@
     ]
   }
 }
 
 if (is_android) {
   android_library("java") {
     java_files = [ "android/java/src/org/chromium/components/external_video_surface/ExternalVideoSurfaceContainer.java" ]
     deps = [
       "//base:base_java",
       "//content/public/android:content_java",
+      "//ui/android:ui_java",
     ]
   }
   generate_jni("jni_headers") {
     sources = [
       "android/java/src/org/chromium/components/external_video_surface/ExternalVideoSurfaceContainer.java",
     ]
     jni_package = "external_video_surface"
   }
 }