Pepper and WebKit API change to support a plugin knowing if a scrollbar is an overlay one.

ppapi/cpp/dev/scrollbar_dev.h

Index: ppapi/cpp/dev/scrollbar_dev.h
===================================================================
--- ppapi/cpp/dev/scrollbar_dev.h	(revision 95420)
+++ ppapi/cpp/dev/scrollbar_dev.h	(working copy)
@@ -11,6 +11,7 @@
 namespace pp {
 
 class Instance;
+class ScrollbarGroup_Dev;
 
 // This class allows a plugin to use the browser's scrollbar widget.
 class Scrollbar_Dev : public Widget_Dev {
@@ -19,13 +20,16 @@
   Scrollbar_Dev() {}
 
   explicit Scrollbar_Dev(PP_Resource resource);
-  Scrollbar_Dev(const Instance& instance, bool vertical);
+  Scrollbar_Dev(const Instance& instance,
+                const ScrollbarGroup_Dev& scrollbar_group,
+                bool vertical);
   Scrollbar_Dev(const Scrollbar_Dev& other);
 
   Scrollbar_Dev& operator=(const Scrollbar_Dev& other);
 
   // PPB_Scrollbar methods:
   uint32_t GetThickness();
+  bool IsOverlay();
   uint32_t GetValue();
   void SetValue(uint32_t value);
   void SetDocumentSize(uint32_t size);