Add option to export tracing events to ETW.

base/trace_event/etw_manifest/etw_manifest.gyp

+# Copyright 2015 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.
+{
+  'targets': [
+    {
+      # GN version: //base/trace_event/etw_manifest/BUILD.gn
+      'target_name': 'etw_manifest',
+      'type': 'static_library',
+      'conditions': [
+        ['OS=="win"', {
+          'sources': [
+            'chrome_events_win.man',
+          ],
+          'variables': {
+            'man_output_dir': '<(SHARED_INTERMEDIATE_DIR)/base/trace_event/etw_manifest',
+          },
+          'rules': [{
+            # Rule to run the message compiler.
+            'rule_name': 'message_compiler',
+            'extension': 'man',
+            'outputs': [
+              '<(man_output_dir)/chrome_events_win.h',
+              '<(man_output_dir)/chrome_events_win.rc',
+            ],
+            'action': [
+              'mc.exe',
+              '-h', '<(man_output_dir)',
+              '-r', '<(man_output_dir)/.',

[scottmg, 2015/04/10 22:41:57]

Actually, sorry. Why do you need the trailing "/."? There was a bug in MSVS
actions long ago for that, be we don't need that any more.

+              '-um',
+              '<(RULE_INPUT_PATH)',
+            ],
+            'message': 'Running message compiler on <(RULE_INPUT_PATH)',
+          }],
+        }],
+      ],
+    }
+  ]
+}