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

ppapi/cpp/file_io.cc

Index: ppapi/cpp/file_io.cc
diff --git a/ppapi/cpp/file_io.cc b/ppapi/cpp/file_io.cc
index 09354d5a69d3207e3f3b2af0a85704856acbb43a..399c4300566a44b2331ae996646e75c0b1bd9b72 100644
--- a/ppapi/cpp/file_io.cc
+++ b/ppapi/cpp/file_io.cc
@@ -8,7 +8,7 @@
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/cpp/completion_callback.h"
 #include "ppapi/cpp/file_ref.h"
-#include "ppapi/cpp/instance.h"
+#include "ppapi/cpp/instance_handle.h"
 #include "ppapi/cpp/module.h"
 #include "ppapi/cpp/module_impl.h"
 
@@ -25,11 +25,11 @@ template <> const char* interface_name<PPB_FileIO>() {
 FileIO::FileIO() {
 }
 
-FileIO::FileIO(Instance* instance) {
+FileIO::FileIO(const InstanceHandle& instance) {
   if (!has_interface<PPB_FileIO>())
     return;
   PassRefFromConstructor(get_interface<PPB_FileIO>()->Create(
-      instance->pp_instance()));
+      instance.pp_instance()));
 }
 
 FileIO::FileIO(const FileIO& other)