events: Create a separate platforms target.

ui/events/platform/x11/x11_events_platform.gyp

+# 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.
+
+{
+  'variables': {
+    'chromium_code': 1,
+  },
+  'targets': [{
+    'target_name': 'x11_events_platform',
+    'type': '<(component)',
+    'defines': [
+      'EVENTS_IMPLEMENTATION',
+    ],
+    'dependencies': [
+      '../../../../build/linux/system.gyp:x11',
+      '../../../gfx/x/gfx_x11.gyp:gfx_x11',
+      '../../events.gyp:events',
+      '../events_platform.gyp:events_platform',
+    ],
+    'sources': [
+      'x11_event_source.cc',
+      'x11_event_source.h',
+      'x11_event_source_glib.cc',
+      'x11_event_source_libevent.cc',
+    ],
+    'conditions': [
+      ['use_glib==1', {
+        'dependencies': [
+          '../../../../build/linux/system.gyp:glib',
+        ],
+        'sources!': [
+          'x11_event_source_libevent.cc',
+        ],
+      }, {
+        # use_glib == 0
+        'sources!': [
+          'x11_event_source_glib.cc',
+        ],
+      }],
+    ],
+  }],
+}