libcros: Watch for display brightness changes.

chromeos_brightness.h

Index: chromeos_brightness.h
diff --git a/chromeos_brightness.h b/chromeos_brightness.h
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+// Copyright (c) 2010 The Chromium OS 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 CHROMEOS_BRIGHTNESS_H_
+#define CHROMEOS_BRIGHTNESS_H_
+
+namespace chromeos {
+
+// Signature of function invoked to handle brightness changes.  Arguments are
+// the object passed to MonitorBrightness() and the current brightness level
+// (between 0 and 100, inclusive).  This is currently only invoked in response
+// to user-requested brightness changes, i.e. caused by the brightness keys.
+typedef void (*BrightnessMonitorFunction)(void*, int);
+
+class OpaqueBrightnessConnection;
+typedef OpaqueBrightnessConnection* BrightnessConnection;
+
+// Register a handler that will be called when the screen brightness changes.
+extern BrightnessConnection (*MonitorBrightness)(
+    BrightnessMonitorFunction monitor_function,
+    void* object);
+
+// Unregister the handler.  Takes the BrightnessConnection returned by
+// MonitorBrightness().
+extern void (*DisconnectBrightness)(BrightnessConnection connection);
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_BRIGHTNESS_H_