Fix some leaks and failures under valgrind in JS extensions unit tests.

extensions/renderer/api/serial/serial_api_unittest.cc

Index: extensions/renderer/api/serial/serial_api_unittest.cc
diff --git a/extensions/renderer/api/serial/serial_api_unittest.cc b/extensions/renderer/api/serial/serial_api_unittest.cc
index 799ecbb81fe53f69998894a3c20b46dd3289f5a0..27c14f357d6b2640bc3d999c575811d6c649bf74 100644
--- a/extensions/renderer/api/serial/serial_api_unittest.cc
+++ b/extensions/renderer/api/serial/serial_api_unittest.cc
@@ -313,12 +313,6 @@ class SerialApiTest : public ApiTestBase {
         &SerialApiTest::CreateSerialService, base::Unretained(this)));
   }
 
-  virtual void TearDown() OVERRIDE {
-    if (io_handler_.get())
-      EXPECT_TRUE(io_handler_->HasOneRef());
-    ApiTestBase::TearDown();
-  }
-
   scoped_refptr<TestIoHandlerBase> io_handler_;
 
  private: