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

ppapi/cpp/graphics_2d.cc

Index: ppapi/cpp/graphics_2d.cc
diff --git a/ppapi/cpp/graphics_2d.cc b/ppapi/cpp/graphics_2d.cc
index c0ea84ee3a13905647759a7b52cdd4ef00e5f095..1ae976bc117d17df45caa0bda7c47a1da5600e94 100644
--- a/ppapi/cpp/graphics_2d.cc
+++ b/ppapi/cpp/graphics_2d.cc
@@ -8,7 +8,7 @@
 #include "ppapi/c/ppb_graphics_2d.h"
 #include "ppapi/cpp/completion_callback.h"
 #include "ppapi/cpp/image_data.h"
-#include "ppapi/cpp/instance.h"
+#include "ppapi/cpp/instance_handle.h"
 #include "ppapi/cpp/module.h"
 #include "ppapi/cpp/module_impl.h"
 #include "ppapi/cpp/point.h"
@@ -32,14 +32,14 @@ Graphics2D::Graphics2D(const Graphics2D& other)
       size_(other.size_) {
 }
 
-Graphics2D::Graphics2D(Instance* instance,
+Graphics2D::Graphics2D(const InstanceHandle& instance,
                        const Size& size,
                        bool is_always_opaque)
     : Resource() {
   if (!has_interface<PPB_Graphics2D>())
     return;
   PassRefFromConstructor(get_interface<PPB_Graphics2D>()->Create(
-      instance->pp_instance(),
+      instance.pp_instance(),
       &size.pp_size(),
       PP_FromBool(is_always_opaque)));
   if (!is_null()) {