Fix compilation error by unused functions under ceratin build configuration.

chromeos/disks/disk_mount_manager_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 374 matching lines @@
   // Pointer to the manager object to which this |Observer| is registered.
   const DiskMountManager* manager_;
 
   // Records all invocations.
   std::vector<std::unique_ptr<ObserverEvent>> events_;
 };
 
 // Shift operators of ostream.
 // Needed to print values in case of EXPECT_* failure in gtest.
 std::ostream& operator<<(std::ostream& stream,
-                         const DeviceEvent& device_event) {
-  return stream << device_event.DebugString();
-}
-
-std::ostream& operator<<(std::ostream& stream, const DiskEvent& disk_event) {
-  return stream << disk_event.DebugString();
-}
-
-std::ostream& operator<<(std::ostream& stream,
                          const FormatEvent& format_event) {
   return stream << format_event.DebugString();
 }
 
-std::ostream& operator<<(std::ostream& stream, const MountEvent& mount_event) {
-  return stream << mount_event.DebugString();
-}
-
 class DiskMountManagerTest : public testing::Test {
  public:
   DiskMountManagerTest() {}
   ~DiskMountManagerTest() override {}
 
   // Sets up test dbus tread manager and disks mount manager.
   // Initializes disk mount manager disks and mount points.
   // Adds a test observer to the disk mount manager.
   void SetUp() override {
     fake_cros_disks_client_ = new FakeCrosDisksClient;
@@ skipping 485 matching lines @@
   ASSERT_EQ(1U, observer_->GetEventCount());
   VerifyMountEvent(observer_->GetMountEvent(0), DiskMountManager::MOUNTING,
                    chromeos::MOUNT_ERROR_NONE, kReadOnlyMountpath);
   const DiskMountManager::DiskMap& disks = manager->disks();
   ASSERT_GT(disks.count(kReadOnlyDeviceSource), 0U);
   // The mounted disk should preserve the read-only flag of the block device.
   EXPECT_TRUE(disks.find(kReadOnlyDeviceSource)->second->is_read_only());
 }
 
 }  // namespace