Add metrics for the number of attached displays.

ui/gfx/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/ui.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
@@ skipping 257 matching lines @@
     ]
   } else {
     deps += [ "//third_party:jpeg" ]
   }
 
   # Android.
   if (is_android) {
     sources -= [
       "animation/throb_animation.cc",
       "canvas_skia.cc",
-      "display_observer.cc",
       "selection_model.cc",
     ]
 
     if (use_aura) {
       sources -= [ "screen_android.cc" ]
     } else {
       sources -= [ "path.cc" ]
     }
 
     # TODO(GYP) re-enable when base_java exists.
@@ skipping 277 matching lines @@
 if (is_android) {
   generate_jni("gfx_jni_headers") {
     sources = [
       "../android/java/src/org/chromium/ui/gfx/BitmapHelper.java",
       "../android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java",
       "../android/java/src/org/chromium/ui/gfx/ViewConfigurationHelper.java",
     ]
     jni_package = "gfx"
   }
 }