Gamepad API: add support for gamepadconnected and gamepaddisconnected events

public/platform/WebGamepads.h

Index: public/platform/WebGamepads.h
diff --git a/public/platform/WebGamepads.h b/public/platform/WebGamepads.h
index 08b067988c7dbc632766a77a52a82ef17fb150f1..a2e9ea10d79a6f64240cf552f4faddd4f2402626 100644
--- a/public/platform/WebGamepads.h
+++ b/public/platform/WebGamepads.h
@@ -32,6 +32,15 @@
 
 namespace blink {
 
+class WebGamepadListener {
+public:
+    virtual void onGamepadConnected(unsigned index, const blink::WebGamepad&) = 0;
+    virtual void onGamepadDisconnected(unsigned index, const blink::WebGamepad&) = 0;
+
+protected:
+    virtual ~WebGamepadListener() { }
+};
+
 #pragma pack(push, 1)
 
 // This structure is intentionally POD and fixed size so that it can be stored