[serializer] API to re-use global proxy in v8::Context::FromSnapshot.

test/cctest/test-serialize.cc

 // Copyright 2007-2010 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 2425 matching lines @@
         v8::TryCatch try_catch(isolate);
         CHECK(CompileRun("x").IsEmpty());
         CHECK(try_catch.HasCaught());
       }
       {
         // Create a new context from first additional context snapshot. This
         // will use the global object from the snapshot, including interceptor.
         v8::HandleScope handle_scope(isolate);
         v8::Local<v8::Context> context =
             v8::Context::FromSnapshot(isolate, 0).ToLocalChecked();
-        v8::Context::Scope context_scope(context);
-        ExpectInt32("f()", 42);
-        ExpectInt32("g()", 12);
-        ExpectInt32("h()", 13);
-        ExpectInt32("i()", 24);
-        ExpectInt32("j()", 25);
-        ExpectInt32("o.p", 8);
-        ExpectInt32("x", 2016);
-        ExpectInt32("y", 2017);
+        {
+          v8::Context::Scope context_scope(context);
+          ExpectInt32("f()", 42);
+          ExpectInt32("g()", 12);
+          ExpectInt32("h()", 13);
+          ExpectInt32("i()", 24);
+          ExpectInt32("j()", 25);
+          ExpectInt32("o.p", 8);
+          ExpectInt32("x", 2016);
+        }
+
+        v8::Local<v8::Object> global = context->Global();
+        context->DetachGlobal();
+
+        // New context, but reuse global proxy.
+        v8::ExtensionConfiguration* no_extensions = nullptr;
+        v8::Local<v8::Context> context2 =
+            v8::Context::FromSnapshot(isolate, 0, no_extensions, global)
+                .ToLocalChecked();
+        {
+          v8::Context::Scope context_scope(context2);
+          ExpectInt32("f()", 42);
+          ExpectInt32("g()", 12);
+          ExpectInt32("h()", 13);
+          ExpectInt32("i()", 24);
+          ExpectInt32("j()", 25);
+          ExpectInt32("o.p", 8);
+          ExpectInt32("x", 2016);
+        }
+
+        CHECK(context2->Global()->Equals(context2, global).FromJust());
       }
     }
     isolate->Dispose();
   }
   delete[] blob.data;
 }
 
 TEST(SerializationMemoryStats) {
   FLAG_profile_deserialization = true;
   FLAG_always_opt = false;
   v8::StartupData blob = v8::V8::CreateSnapshotDataBlob();
   delete[] blob.data;
 }