Fix test-heap/BootstrapperExports on no-snap builds

NOTRY=true
NOTREECHECKS=true
TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/1137143003

Cr-Commit-Position: refs/heads/master@{#28368}

src/bootstrapper.cc

@@ -1923,6 +1923,11 @@ bool Genesis::InstallNatives() {
                                 "container to export to experimental natives");
   native_context()->set_builtin_exports_object(*builtin_exports);
 
+  if (FLAG_expose_natives_as != NULL) {
+    Handle<String> shared_key = factory()->NewStringFromAsciiChecked("shared");
+    JSObject::AddProperty(builtins, shared_key, shared, NONE);
+  }
+
   {  // -- S c r i p t
     // Builtin functions for Script.
     Handle<JSFunction> script_fun = InstallFunction(