base: Remove now-unused MessagePumpObserver.

base/BUILD.gn

 # Copyright (c) 2013 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/rules.gni")
 }
 
@@ skipping 349 matching lines @@
     "message_loop/message_pump_default.cc",
     "message_loop/message_pump_default.h",
     "message_loop/message_pump_glib.cc",
     "message_loop/message_pump_glib.h",
     "message_loop/message_pump_io_ios.cc",
     "message_loop/message_pump_io_ios.h",
     "message_loop/message_pump_libevent.cc",
     "message_loop/message_pump_libevent.h",
     "message_loop/message_pump_mac.h",
     "message_loop/message_pump_mac.mm",
-    "message_loop/message_pump_observer.h",
     "message_loop/message_pump_win.cc",
     "message_loop/message_pump_win.h",
     "metrics/field_trial.cc",
     "metrics/field_trial.h",
     "metrics/sample_map.cc",
     "metrics/sample_map.h",
     "metrics/sample_vector.cc",
     "metrics/sample_vector.h",
     "metrics/bucket_ranges.cc",
     "metrics/bucket_ranges.h",
@@ skipping 1072 matching lines @@
 
   unittest_apk("base_unittests_apk") {
     deps = [
       ":base_java",
       ":base_java_unittest_support",
       ":base_unittests",
     ]
     unittests_dep = ":base_unittests"
   }
 }