Re-add snap-back behavior (Blink side)

public/platform/Platform.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 67 matching lines @@
 class WebMediaStreamCenterClient;
 class WebMessagePortChannel;
 class WebMimeRegistry;
 class WebPluginListBuilder;
 class WebPrescientNetworking;
 class WebPublicSuffixList;
 class WebRTCPeerConnectionHandler;
 class WebRTCPeerConnectionHandlerClient;
 class WebSandboxSupport;
 class WebScreenOrientationListener;
+class WebScrollbarBehavior;
 class WebSocketHandle;
 class WebSocketStreamHandle;
 class WebSpeechSynthesizer;
 class WebSpeechSynthesizerClient;
 class WebStorageNamespace;
 struct WebFloatPoint;
 class WebThemeEngine;
 class WebThread;
 class WebURL;
 class WebURLLoader;
@@ skipping 296 matching lines @@
     // Returns true on success.
     virtual bool loadAudioResource(WebAudioBus* destinationBus, const char* audioFileData, size_t dataSize, double sampleRate) { return false; }
 
 
     // Screen -------------------------------------------------------------
 
     // Supplies the system monitor color profile.
     virtual void screenColorProfile(WebVector<char>* profile) { }
 
 
+    // Scrollbar ----------------------------------------------------------
+
+    // Must return non-null.
+    virtual WebScrollbarBehavior* scrollbarBehavior() { return 0; }
+
+
     // Sudden Termination --------------------------------------------------
 
     // Disable/Enable sudden termination.
     virtual void suddenTerminationChanged(bool enabled) { }
 
 
     // System --------------------------------------------------------------
 
     // Returns a value such as "en-US".
     virtual WebString defaultLocale() { return WebString(); }
@@ skipping 218 matching lines @@
     virtual WebDatabaseObserver* databaseObserver() { return 0; }
 
 
 protected:
     virtual ~Platform() { }
 };
 
 } // namespace blink
 
 #endif