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

ppapi/cpp/dev/buffer_dev.h

Index: ppapi/cpp/dev/buffer_dev.h
diff --git a/ppapi/cpp/dev/buffer_dev.h b/ppapi/cpp/dev/buffer_dev.h
index 9e9ac813ce5e4360d1f18f4d35aea185a9e594e2..da89cbaee58ca83992dbe9dc4898a1251c35720d 100644
--- a/ppapi/cpp/dev/buffer_dev.h
+++ b/ppapi/cpp/dev/buffer_dev.h
@@ -9,7 +9,7 @@
 
 namespace pp {
 
-class Instance;
+class InstanceHandle;
 
 class Buffer_Dev : public Resource {
  public:
@@ -20,7 +20,7 @@ class Buffer_Dev : public Resource {
 
   // Creates & Maps a new Buffer in the browser with the given size. The
   // resulting object will be is_null() if either Create() or Map() fails.
-  Buffer_Dev(Instance* instance, uint32_t size);
+  Buffer_Dev(const InstanceHandle& instance, uint32_t size);
 
   // Unmap the underlying shared memory.
   virtual ~Buffer_Dev();