Only reference constant root list entries in the snapshot.

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5074 matching lines @@
 #ifdef DEBUG
 TEST(PathTracer) {
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
 
   v8::Local<v8::Value> result = CompileRun("'abc'");
   Handle<Object> o = v8::Utils::OpenHandle(*result);
   CcTest::i_isolate()->heap()->TracePathToObject(*o);
 }
 #endif  // DEBUG
+
+
+TEST(WritableVsImmortalRoots) {
+  for (int i = 0; i < Heap::kStrongRootListLength; ++i) {
+    Heap::RootListIndex root_index = static_cast<Heap::RootListIndex>(i);
+    bool writable = Heap::RootCanBeWrittenAfterInitialization(root_index);
+    bool immortal = Heap::RootIsImmortalImmovable(root_index);
+    // A root value can be writable, immortal, or neither, but not both.
+    CHECK(!immortal || !writable);
+  }
+}