Convert resources to take an instance key instead of an Instance*.

ppapi/cpp/dev/scrollbar_dev.h

Index: ppapi/cpp/dev/scrollbar_dev.h
diff --git a/ppapi/cpp/dev/scrollbar_dev.h b/ppapi/cpp/dev/scrollbar_dev.h
index f7944e984e884cd80a0fdccda09d75187343cd10..fabbbd7f471bd6c8d24931ffc4abe8f7bca4e8ba 100644
--- a/ppapi/cpp/dev/scrollbar_dev.h
+++ b/ppapi/cpp/dev/scrollbar_dev.h
@@ -10,7 +10,7 @@
 
 namespace pp {
 
-class Instance;
+class InstanceHandle;
 
 // This class allows a plugin to use the browser's scrollbar widget.
 class Scrollbar_Dev : public Widget_Dev {
@@ -19,7 +19,7 @@ class Scrollbar_Dev : public Widget_Dev {
   Scrollbar_Dev() {}
 
   explicit Scrollbar_Dev(PP_Resource resource);
-  Scrollbar_Dev(const Instance& instance, bool vertical);
+  Scrollbar_Dev(const InstanceHandle& instance, bool vertical);
   Scrollbar_Dev(const Scrollbar_Dev& other);
 
   Scrollbar_Dev& operator=(const Scrollbar_Dev& other);