Try fix win64 build.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index ff685724a49bd269b836dba953d4c904de55e9a7..1f125026843f98e7228de81f58d13cca725f66f0 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -1354,7 +1354,8 @@ static Handle<JSObject> ResolveCustomCallGeneratorHolder(
         GetProperty(global, Factory::LookupAsciiSymbol(holder_expr)));
   }
   ASSERT_EQ(".prototype", period_pos);
-  Vector<const char> property(holder_expr, period_pos - holder_expr);
+  Vector<const char> property(holder_expr,
+                              static_cast<int>(period_pos - holder_expr));
   Handle<JSFunction> function = Handle<JSFunction>::cast(
       GetProperty(global, Factory::LookupSymbol(property)));
   return Handle<JSObject>(JSObject::cast(function->prototype()));