Allow null in Dart_SetRootLibrary.

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "lib/stacktrace.h"
@@ skipping 5317 matching lines @@
 DART_EXPORT Dart_Handle Dart_RootLibrary() {
   Thread* thread = Thread::Current();
   Isolate* isolate = thread->isolate();
   CHECK_ISOLATE(isolate);
   return Api::NewHandle(thread, isolate->object_store()->root_library());
 }
 
 
 DART_EXPORT Dart_Handle Dart_SetRootLibrary(Dart_Handle library) {
   DARTSCOPE(Thread::Current());
-  const Library& lib = Api::UnwrapLibraryHandle(Z, library);
-  if (lib.IsNull()) {
-    RETURN_TYPE_ERROR(Z, library, Library);
+  const Object& obj = Object::Handle(Z, Api::UnwrapHandle(library));
+  if (obj.IsNull() || obj.IsLibrary()) {
+    Library& lib = Library::Handle(Z);
+    lib ^= obj.raw();
+    T->isolate()->object_store()->set_root_library(lib);
+    return library;
   }
-  Isolate* isolate = Isolate::Current();
-  isolate->object_store()->set_root_library(lib);
-  return library;
+  RETURN_TYPE_ERROR(Z, library, Library);
 }
 
 
 DART_EXPORT Dart_Handle Dart_GetClass(Dart_Handle library,
                                       Dart_Handle class_name) {
   DARTSCOPE(Thread::Current());
   const Library& lib = Api::UnwrapLibraryHandle(Z, library);
   if (lib.IsNull()) {
     RETURN_TYPE_ERROR(Z, library, Library);
   }
@@ skipping 1084 matching lines @@
 
 DART_EXPORT bool Dart_IsPrecompiledRuntime() {
 #if defined(DART_PRECOMPILED_RUNTIME)
   return true;
 #else
   return false;
 #endif
 }
 
 }  // namespace dart