Change scoped_ptr::reset()'s behaviour to match unique_ptr.

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..71d995c452e826ad1faeb28f315433077f338e88 100644
--- a/base/memory/scoped_ptr_unittest.cc
+++ b/base/memory/scoped_ptr_unittest.cc
@@ -693,3 +693,26 @@ 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 calling reset(). This will cause |a| (and hence, |a.b|)
+  // to be deleted before the call to reset() returns. This tests that the
+  // implementation of scoped_ptr::reset() doesn't access |this| after it
+  // deletes the underlying pointer. This behaviour is consistent with the
+  // definition of unique_ptr::reset in C++11.
+  a->b.reset();
+}