Fix for issue 5223 : Import 'dart:core' implicitly only if it has not been

runtime/vm/object.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 2088 matching lines @@
   RawArray* LoadedScripts() const;
 
   void AddAnonymousClass(const Class& cls) const;
 
   // Library imports.
   void AddImport(const Library& library) const;
   RawLibrary* LookupImport(const String& url) const;
   intptr_t num_imports() const { return raw_ptr()->num_imports_; }
   RawLibrary* ImportAt(intptr_t index) const;
   RawLibraryPrefix* ImportPrefixAt(intptr_t index) const;
+  bool ImportsCorelib() const;
 
   RawFunction* LookupFunctionInSource(const String& script_url,
                                       intptr_t line_number) const;
   RawFunction* LookupFunctionInScript(const Script& script,
                                       intptr_t token_pos) const;
 
   // Resolving native methods for script loaded in the library.
   Dart_NativeEntryResolver native_entry_resolver() const {
     return raw_ptr()->native_entry_resolver_;
   }
@@ skipping 12 matching lines @@
 
   void Register() const;
 
   bool IsDebuggable() const {
     return raw_ptr()->debuggable_;
   }
   void set_debuggable(bool value) const {
     raw_ptr()->debuggable_ = value;
   }
 
+  bool IsCoreLibrary() const {
+    return raw() == CoreLibrary();
+  }
+
   static RawLibrary* LookupLibrary(const String& url);
   static RawLibrary* GetLibrary(intptr_t index);
   static bool IsKeyUsed(intptr_t key);
 
   static void InitCoreLibrary(Isolate* isolate);
   static void InitMathLibrary(Isolate* isolate);
   static void InitIsolateLibrary(Isolate* isolate);
   static void InitMirrorsLibrary(Isolate* isolate);
   static void InitScalarlistLibrary(Isolate* isolate);
   static void InitNativeWrappersLibrary(Isolate* isolate);
@@ skipping 3494 matching lines @@
     if (this->CharAt(i) != str.CharAt(begin_index + i)) {
       return false;
     }
   }
   return true;
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_