For unit tests, track additions to AtExitManager and warn.

content/test/test_renderer_host.cc

Index: content/test/test_renderer_host.cc
diff --git a/content/test/test_renderer_host.cc b/content/test/test_renderer_host.cc
index ee1adf2aa98e029b299646773de98e317e810675..f843b069b75d93c70f7b3b8c1beea0cffe575200 100644
--- a/content/test/test_renderer_host.cc
+++ b/content/test/test_renderer_host.cc
@@ -132,6 +132,8 @@ void RenderViewHostTestHarness::SetUp() {
   aura_test_helper_->SetUp();
 #endif
   SetContents(CreateTestWebContents());
+
+  base::UnitTest::SetUp();
 }
 
 void RenderViewHostTestHarness::TearDown() {
@@ -146,6 +148,8 @@ void RenderViewHostTestHarness::TearDown() {
   // Release the browser context on the UI thread.
   message_loop_.DeleteSoon(FROM_HERE, browser_context_.release());
   message_loop_.RunAllPending();
+
+  base::UnitTest::TearDown();
 }
 
 void RenderViewHostTestHarness::SetRenderProcessHostFactory(