Add d8 functionality for switching between realms (a.k.a. contexts)

src/d8.h

Index: src/d8.h
diff --git a/src/d8.h b/src/d8.h
index 2789c076383be2448d4dacaa5afdf77476e4c37b..4d9504f0d45c9656c9e52b3c58a7b83d9521774d 100644
--- a/src/d8.h
+++ b/src/d8.h
@@ -298,6 +298,19 @@ class Shell : public i::AllStatic {
 #endif  // ENABLE_DEBUGGER_SUPPORT
 #endif  // V8_SHARED
 
+  static Handle<Value> RealmCurrent(const Arguments& args);
+  static Handle<Value> RealmOwner(const Arguments& args);
+  static Handle<Value> RealmGlobal(const Arguments& args);
+  static Handle<Value> RealmCreate(const Arguments& args);
+  static Handle<Value> RealmDispose(const Arguments& args);
+  static Handle<Value> RealmSwitch(const Arguments& args);
+  static Handle<Value> RealmEval(const Arguments& args);
+  static Handle<Value> RealmSharedGet(Local<String> property,
+                                      const AccessorInfo& info);
+  static void RealmSharedSet(Local<String> property,
+                             Local<Value> value,
+                             const AccessorInfo& info);
+
   static Handle<Value> Print(const Arguments& args);
   static Handle<Value> Write(const Arguments& args);
   static Handle<Value> Quit(const Arguments& args);