Decouple Power Monitor from //content.

device/power_monitor/power_monitor_export.h

Index: device/power_monitor/power_monitor_export.h
diff --git a/device/power_monitor/power_monitor_export.h b/device/power_monitor/power_monitor_export.h
new file mode 100644
index 0000000000000000000000000000000000000000..ff6e367c57bde889e42cf012b1235896205e63dd
--- /dev/null
+++ b/device/power_monitor/power_monitor_export.h
@@ -0,0 +1,29 @@
+// Copyright (c) 2016 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.
+
+#ifndef DEVICE_POWER_MONITOR_POWER_MONITOR_EXPORT_H_
+#define DEVICE_POWER_MONITOR_POWER_MONITOR_EXPORT_H_
+
+#if defined(COMPONENT_BUILD)
+#if defined(WIN32)
+
+#if defined(DEVICE_POWER_MONITOR_IMPLEMENTATION)
+#define DEVICE_POWER_MONITOR_EXPORT __declspec(dllexport)
+#else
+#define DEVICE_POWER_MONITOR_EXPORT __declspec(dllimport)
+#endif  // defined(DEVICE_POWER_MONITOR_IMPLEMENTATION)
+
+#else  // defined(WIN32)
+#if defined(DEVICE_POWER_MONITOR_IMPLEMENTATION)
+#define DEVICE_POWER_MONITOR_EXPORT __attribute__((visibility("default")))
+#else
+#define DEVICE_POWER_MONITOR_EXPORT
+#endif
+#endif
+
+#else  // defined(COMPONENT_BUILD)
+#define DEVICE_POWER_MONITOR_EXPORT
+#endif
+
+#endif  // DEVICE_POWER_MONITOR_POWER_MONITOR_EXPORT_H_