Start checking inputs to dart api functions.

runtime/vm/dart_api_impl.h

Index: runtime/vm/dart_api_impl.h
===================================================================
--- runtime/vm/dart_api_impl.h	(revision 1707)
+++ runtime/vm/dart_api_impl.h	(working copy)
@@ -6,16 +6,14 @@
 #define VM_DART_API_IMPL_H_
 
 #include "vm/allocation.h"
+#include "vm/object.h"
 
 namespace dart {
 
 class ApiState;
 class LocalHandle;
-class Object;
 class PersistentHandle;
-class RawObject;
 
-
 #define DARTSCOPE(isolate)                                                    \
   ASSERT(isolate != NULL);                                                    \
   Zone zone(isolate);                                                         \
@@ -29,6 +27,13 @@
   // Unwraps the raw object from the handle.
   static RawObject* UnwrapHandle(Dart_Handle object);
 
+  // Unwraps a raw Type from the handle.  The handle will be null if
+  // the object was not of the requested Type.
+#define DECLARE_UNWRAP(Type)                                                  \
+  static const Type& Unwrap##Type##Handle(Dart_Handle object);
+  CLASS_LIST_NO_OBJECT(DECLARE_UNWRAP)
+#undef DECLARE_UNWRAP
+
   // Validates and converts the passed in handle as a local handle.
   static LocalHandle* UnwrapAsLocalHandle(const ApiState& state,
                                           Dart_Handle object);