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

runtime/vm/code_generator_test.cc

 // 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.
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_IA32) || defined(TARGET_ARCH_X64)
 
 #include "vm/ast.h"
 #include "vm/assembler.h"
@@ skipping 250 matching lines @@
   UnaryOpNode* neg_node = new UnaryOpNode(kPos, Token::kSUB, a);
   node_seq->Add(new ReturnNode(kPos, neg_node));
 }
 CODEGEN_TEST_RUN(DoubleUnaryOpCodegen, Double::New(-12.0))
 
 
 static Library& MakeTestLibrary(const char* url) {
   const String& lib_url = String::ZoneHandle(Symbols::New(url));
   Library& lib = Library::ZoneHandle(Library::New(lib_url));
   lib.Register();
+  Library& core_lib = Library::Handle(Library::CoreLibrary());
+  ASSERT(!core_lib.IsNull());
+  lib.AddImport(core_lib);
   return lib;
 }
 
 
 static RawClass* LookupClass(const Library& lib, const char* name) {
   const String& cls_name = String::ZoneHandle(Symbols::New(name));
   return lib.LookupClass(cls_name);
 }
 
 
@@ skipping 230 matching lines @@
   app_lib ^= libs.At(num_libs - 1);
   ASSERT(!app_lib.IsNull());
   const Class& cls = Class::Handle(
       app_lib.LookupClass(String::Handle(Symbols::New("A"))));
   EXPECT_EQ(cls.raw(), result.clazz());
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32 || defined(TARGET_ARCH_X64)