Add setBatteryListener into Platform.

public/platform/Platform.h

Index: public/platform/Platform.h
diff --git a/public/platform/Platform.h b/public/platform/Platform.h
index 5682f3b71b830bb9a438f994ec089eb7e61fdb51..ab1c577a75539d67a9d5f60e17288b0570ce7775 100644
--- a/public/platform/Platform.h
+++ b/public/platform/Platform.h
@@ -55,6 +55,7 @@ class GrContext;
 namespace blink {
 
 class WebAudioBus;
+class WebBatteryStatusListener;
 class WebBlobRegistry;
 class WebContentDecryptionModule;
 class WebClipboard;
@@ -160,6 +161,12 @@ public:
     virtual WebMIDIAccessor* createMIDIAccessor(WebMIDIAccessorClient*) { return 0; }
 
 
+    // Battery -------------------------------------------------------------
+
+    // Sets the listener for watching battery status updates.
+    virtual void setBatteryStatusListener(blink::WebBatteryStatusListener*) { }
+
+
     // Blob ----------------------------------------------------------------
 
     // Must return non-null.