Call reset(nullptr) in scoped_ptr's.

base/memory/scoped_ptr_unittest.cc

Index: base/memory/scoped_ptr_unittest.cc
diff --git a/base/memory/scoped_ptr_unittest.cc b/base/memory/scoped_ptr_unittest.cc
index 766f4444001e828cd077ca39b85c7dd326779c65..bc6880dba89b2b1a53e0453f07418d156b70424e 100644
--- a/base/memory/scoped_ptr_unittest.cc
+++ b/base/memory/scoped_ptr_unittest.cc
@@ -693,3 +693,24 @@ TEST(ScopedPtrTest, LoggingDoesntConvertToBoolean) {
 
   EXPECT_EQ(s2.str(), s1.str());
 }
+
+TEST(ScopedPtrTest, ReferenceCycle) {
+  struct StructB;
+  struct StructA {
+    scoped_ptr<StructB> b;
+  };
+
+  struct StructB {
+    scoped_ptr<StructA> a;
+  };
+
+  // Create a reference cycle.
+  StructA* a = new StructA;
+  a->b.reset(new StructB);
+  a->b->a.reset(a);
+
+  // Break the cycle by deleting a.
+  // Note, the cycle cannot currently be broken by calling reset, because reset
+  // sets the new value after deleting the object.
+  delete a;
+}