Add GN buildfiles for ui/compositor and snapshot.

ui/base/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")
 }
 
-component("ui_base") {
+component("base") {
+  output_name = "ui_base"
   sources = [
     "accelerators/accelerator.cc",
     "accelerators/accelerator.h",
     "accelerators/accelerator_manager.cc",
     "accelerators/accelerator_manager.h",
     "accelerators/menu_label_accelerator_util_linux.cc",
     "accelerators/menu_label_accelerator_util_linux.h",
     "accelerators/platform_accelerator.h",
     "accelerators/platform_accelerator_cocoa.h",
     "accelerators/platform_accelerator_cocoa.mm",
@@ skipping 529 matching lines @@
       "../android/java/src/org/chromium/ui/base/DeviceFormFactor.java",
       "../android/java/src/org/chromium/ui/base/LocalizationUtils.java",
       "../android/java/src/org/chromium/ui/base/SelectFileDialog.java",
       "../android/java/src/org/chromium/ui/base/TouchDevice.java",
       "../android/java/src/org/chromium/ui/base/ViewAndroid.java",
       "../android/java/src/org/chromium/ui/base/WindowAndroid.java",
     ]
     jni_package = "base"
   }
 }