Refactor the way singleton-style resources are exposed via PPB_Instance

ppapi/thunk/enter.h

Index: ppapi/thunk/enter.h
diff --git a/ppapi/thunk/enter.h b/ppapi/thunk/enter.h
index 276f0457647d07d08f367cbced88430fdf781c3c..094d10e484a7d3ff63bf58b7b39c4c5a655afd2f 100644
--- a/ppapi/thunk/enter.h
+++ b/ppapi/thunk/enter.h
@@ -245,6 +245,47 @@ class PPAPI_THUNK_EXPORT EnterInstanceNoLock
   PPB_Instance_API* functions_;
 };
 
+// EnterInstanceAPI ------------------------------------------------------------
+
+template<typename ApiT, bool lock_on_entry = true>
+class PPAPI_THUNK_EXPORT EnterInstanceAPI
+    : public subtle::EnterBase,
+      public subtle::LockOnEntry<lock_on_entry> {
+ public:
+  EnterInstanceAPI(PP_Instance instance,
+                   SingletonResourceID singleton_resource_id) : EnterBase() {

[yzshen1, 2012/11/20 21:47:25]

We can deduce the SingletonResourceID from ApiT, right?
One way to consider is template specialization.

[raymes, 2012/11/20 23:30:23]

Yes I was considering whether or not I wanted to do it. I think it's better to.
I added constants to the API definitions.

+    functions_ = NULL;
+    PPB_Instance_API* ppb_instance =
+        PpapiGlobals::Get()->GetInstanceAPI(instance);
+    if (ppb_instance) {
+      Resource* resource =
+          ppb_instance->GetSingletonResource(instance, singleton_resource_id);
+      if (resource)
+        functions_ = resource->GetAs<ApiT>();
+    }
+    SetStateForFunctionError(instance, functions_, true);
+  }
+  ~EnterInstanceAPI() {}
+
+  bool succeeded() const { return !!functions_; }
+  bool failed() const { return !functions_; }
+
+  ApiT* functions() { return functions_; }
+
+ private:
+  ApiT* functions_;
+};
+
+template<typename ApiT>
+class PPAPI_THUNK_EXPORT EnterInstanceAPINoLock
+    : public EnterInstanceAPI<ApiT, false> {
+ public:
+  EnterInstanceAPINoLock(PP_Instance instance,
+                         SingletonResourceID singleton_resource_id)
+      : EnterInstanceAPI<ApiT, false>(instance, singleton_resource_id) {
+  }
+};
+
 // EnterResourceCreation -------------------------------------------------------
 
 class PPAPI_THUNK_EXPORT EnterResourceCreation