[serializer] ensure that immortal immovable roots are correctly deserialized.

test/cctest/test-serialize.cc

Index: test/cctest/test-serialize.cc
diff --git a/test/cctest/test-serialize.cc b/test/cctest/test-serialize.cc
index c59dc3b355e0a24519cb43b9abbffe5e75867266..cd349f9d735160753e691473f4b50a4165de434e 100644
--- a/test/cctest/test-serialize.cc
+++ b/test/cctest/test-serialize.cc
@@ -854,6 +854,36 @@ TEST(CustomSnapshotDataBlobWithWarmup) {
   isolate->Dispose();
 }
 
+TEST(CustomSnapshotDataBlobImmortalImmovableRoots) {
+  DisableTurbofan();
+  // Flood the startup snapshot with shared function infos. If they are
+  // serialized before the immortal immovable root, the root will no longer end
+  // up on the first page.
+  Vector<const uint8_t> source =
+      ConstructSource(STATIC_CHAR_VECTOR("var a = [];"),
+                      STATIC_CHAR_VECTOR("a.push(function() {return 7});"),
+                      STATIC_CHAR_VECTOR("\0"), 10000);
+
+  v8::StartupData data = v8::V8::CreateSnapshotDataBlob(
+      reinterpret_cast<const char*>(source.start()));
+
+  v8::Isolate::CreateParams params;
+  params.snapshot_blob = &data;
+  params.array_buffer_allocator = CcTest::array_buffer_allocator();
+
+  v8::Isolate* isolate = v8::Isolate::New(params);
+  {
+    v8::Isolate::Scope i_scope(isolate);
+    v8::HandleScope h_scope(isolate);
+    v8::Local<v8::Context> context = v8::Context::New(isolate);
+    delete[] data.data;  // We can dispose of the snapshot blob now.
+    v8::Context::Scope c_scope(context);
+    CHECK_EQ(7, CompileRun("a[0]()")->Int32Value(context).FromJust());
+  }
+  isolate->Dispose();
+  source.Dispose();
+}
+
 TEST(TestThatAlwaysSucceeds) {
 }