cros: Apply the Init() model to BrightnessLibrary API.

chrome/browser/chromeos/cros/brightness_library.h

Index: chrome/browser/chromeos/cros/brightness_library.h
diff --git a/chrome/browser/chromeos/cros/brightness_library.h b/chrome/browser/chromeos/cros/brightness_library.h
index aae8b29a4943bfcb20ad076069f76eadf4a97470..bcd7f8b2f76560bf1eaea814204d402fbca2e999 100644
--- a/chrome/browser/chromeos/cros/brightness_library.h
+++ b/chrome/browser/chromeos/cros/brightness_library.h
@@ -17,12 +17,14 @@ class BrightnessLibrary {
 
   virtual ~BrightnessLibrary() {}
 
-  virtual void DecreaseScreenBrightness(bool allow_off) = 0;
-  virtual void IncreaseScreenBrightness() = 0;
+  virtual void Init() = 0;
 
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
+  virtual void DecreaseScreenBrightness(bool allow_off) = 0;
+  virtual void IncreaseScreenBrightness() = 0;
+
   // Factory function, creates a new instance and returns ownership.
   // For normal usage, access the singleton via CrosLibrary::Get().
   static BrightnessLibrary* GetImpl(bool stub);