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

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 12667)
+++ runtime/vm/parser.cc	(working copy)
@@ -4219,6 +4219,13 @@
     ParseLibraryNameObsoleteSyntax();
     ParseLibraryImportObsoleteSyntax();
     ParseLibraryIncludeObsoleteSyntax();
+    // Core lib has not been explicitly imported, so we implicitly
+    // import it here.
+    if (!library_.ImportsCorelib()) {
+      Library& core_lib = Library::Handle(Library::CoreLibrary());
+      ASSERT(!core_lib.IsNull());
+      library_.AddImport(core_lib);
+    }
     return;
   }
 
@@ -4240,6 +4247,13 @@
     metadata_pos = TokenPos();
     SkipMetadata();
   }
+  // Core lib has not been explicitly imported, so we implicitly
+  // import it here.
+  if (!library_.ImportsCorelib()) {
+    Library& core_lib = Library::Handle(Library::CoreLibrary());
+    ASSERT(!core_lib.IsNull());
+    library_.AddImport(core_lib);
+  }
   while (IsLiteral("part")) {
     ParseLibraryPart();
     metadata_pos = TokenPos();