Make MockHostResolverProc destructor protected.

components/cronet/stale_host_resolver_unittest.cc

Index: components/cronet/stale_host_resolver_unittest.cc
diff --git a/components/cronet/stale_host_resolver_unittest.cc b/components/cronet/stale_host_resolver_unittest.cc
index cf3d6976952976ab9cff4f4caeafefcb07f5195e..1fb43e081edb96b25caba0da682b1afc4fc93d37 100644
--- a/components/cronet/stale_host_resolver_unittest.cc
+++ b/components/cronet/stale_host_resolver_unittest.cc
@@ -58,8 +58,6 @@ class MockHostResolverProc : public net::HostResolverProc {
  public:
   MockHostResolverProc() : HostResolverProc(nullptr) {}
 
-  ~MockHostResolverProc() override {}
-
   int Resolve(const std::string& hostname,
               net::AddressFamily address_family,
               net::HostResolverFlags host_resolver_flags,
@@ -68,6 +66,9 @@ class MockHostResolverProc : public net::HostResolverProc {
     *address_list = MakeAddressList(kNetworkAddress);
     return net::OK;
   }
+
+ protected:
+  ~MockHostResolverProc() override {}
 };
 
 class StaleHostResolverTest : public testing::Test {