Implement export clause in VM

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 13255)
+++ runtime/vm/object.h	(working copy)
@@ -1839,6 +1839,7 @@
   void AddClass(const Class& cls) const;
   void AddObject(const Object& obj, const String& name) const;
   void ReplaceObject(const Object& obj, const String& name) const;
+  RawObject* LookupExport(const String& name) const;
   RawObject* LookupObject(const String& name) const;
   RawClass* LookupClass(const String& name) const;
   RawClass* LookupClassAllowPrivate(const String& name) const;
@@ -1854,9 +1855,10 @@
 
   void AddAnonymousClass(const Class& cls) const;
 
+  void AddExport(const Namespace& ns) const;
+
   // Library imports.
   void AddImport(const Namespace& ns) const;
-  RawLibrary* LookupImport(const String& url) const;
   intptr_t num_imports() const { return raw_ptr()->num_imports_; }
   RawNamespace* ImportAt(intptr_t index) const;
   RawLibrary* ImportLibraryAt(intptr_t index) const;
@@ -1928,6 +1930,8 @@
     raw_ptr()->num_imports_ = value;
   }
   RawArray* imports() const { return raw_ptr()->imports_; }
+  RawArray* exports() const { return raw_ptr()->exports_; }
+  bool HasExports() const;
   RawArray* loaded_scripts() const { return raw_ptr()->loaded_scripts_; }
   RawArray* dictionary() const { return raw_ptr()->dictionary_; }
   void InitClassDictionary() const;