Revert r18013 failing on Windows.

runtime/vm/dart_api_impl.h

Index: runtime/vm/dart_api_impl.h
===================================================================
--- runtime/vm/dart_api_impl.h	(revision 18014)
+++ runtime/vm/dart_api_impl.h	(working copy)
@@ -58,6 +58,8 @@
   HANDLESCOPE(__temp_isolate__);
 
 
+const char* CheckIsolateState(Isolate *isolate);
+
 void SetupErrorResult(Dart_Handle* handle);
 
 
@@ -96,10 +98,6 @@
       const ApiState& state,
       Dart_Handle object);
 
-  // Returns an Error handle if isolate is in an inconsistent state.
-  // Returns a Success handle when no error condition exists.
-  static Dart_Handle CheckIsolateState(Isolate *isolate);
-
   // Casts the internal Isolate* type to the external Dart_Isolate type.
   static Dart_Isolate CastIsolate(Isolate* isolate);