Make base::PowerMonitor work on Chrome OS.

base/base.gypi

 # Copyright (c) 2012 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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
       'base_i18n_target': 0,
     },
@@ skipping 414 matching lines @@
           'port.h',
           'posix/eintr_wrapper.h',
           'posix/global_descriptors.cc',
           'posix/global_descriptors.h',
           'posix/unix_domain_socket_linux.cc',
           'posix/unix_domain_socket_linux.h',
           'power_monitor/power_monitor.cc',
           'power_monitor/power_monitor.h',
           'power_monitor/power_monitor_device_source_android.cc',
           'power_monitor/power_monitor_device_source_android.h',
+          'power_monitor/power_monitor_device_source_chromeos.cc',
           'power_monitor/power_monitor_device_source.cc',
           'power_monitor/power_monitor_device_source.h',
           'power_monitor/power_monitor_device_source_ios.mm',
           'power_monitor/power_monitor_device_source_mac.mm',
           'power_monitor/power_monitor_device_source_posix.cc',
           'power_monitor/power_monitor_device_source_win.cc',
           'power_monitor/power_monitor_source.cc',
           'power_monitor/power_monitor_source.h',
           'power_monitor/power_observer.h',
           'process/internal_linux.cc',
@@ skipping 386 matching lines @@
               ['include', '^threading/platform_thread_linux\\.cc$'],
             ],
           }],
           ['OS == "android" and <(android_webview_build)==1', {
             'defines': [
                # WebView builds as part of the system which already has sincos;
                # avoid defining it again as it causes a linker warning.
                'ANDROID_SINCOS_PROVIDED',
             ],
           }],
+          ['<(chromeos) == 1', {

[Lei Zhang, 2014/10/06 19:09:28]

In most gyp files we just write chromeos==1. Why do we have to do it in the
early phase here?

[Daniel Erat, 2014/10/06 21:44:13]

i tried that initially, but it produces an error saying that the chromeos
identifier is undefined:

gyp: name 'chromeos' is not defined while evaluating condition 'chromeos == 1'
in /derat/chrome/src/base/base.gyp

in the existing target_condition expressions in this file, pretty much all
user-defined variables (chromeos, desktop_linux, use_glib, os_bsd, etc.) appear
to be using the early/pre-expansion syntax.

my initial thought would be that these variables are only defined after
base.gypi is included in base.gyp, but it doesn't make sense to me why early
expansion would help then (and i get the same "not defined" error when i use
late expansion, oddly). any idea what's going on here?

+            'sources!': [
+              'power_monitor/power_monitor_device_source_posix.cc',
+            ],
+          }],
           ['OS == "ios" and _toolset != "host"', {
             'sources/': [
               # Pull in specific Mac files for iOS (which have been filtered out
               # by file name rules).
               ['include', '^atomicops_internals_mac\\.'],
               ['include', '^base_paths_mac\\.'],
               ['include', '^files/file_util_mac\\.'],
               ['include', '^file_version_info_mac\\.'],
               ['include', '^mac/bundle_locations\\.'],
               ['include', '^mac/foundation_util\\.'],
@@ skipping 147 matching lines @@
           'i18n/time_formatting.h',
           'i18n/timezone.cc',
           'i18n/timezone.h',
           'i18n/utf8_validator_tables.cc',
           'i18n/utf8_validator_tables.h',
         ],
       }]
     ],
   },
 }