Add a feature flag for the new Windows USB backend.

chrome/browser/about_flags.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 "chrome/browser/about_flags.h"
 
 #include <iterator>
 #include <map>
 #include <set>
 #include <utility>
@@ skipping 53 matching lines @@
 #include "components/sync/driver/sync_driver_switches.h"
 #include "components/tracing/common/tracing_switches.h"
 #include "components/translate/core/browser/translate_manager.h"
 #include "components/translate/core/browser/translate_prefs.h"
 #include "components/version_info/version_info.h"
 #include "content/public/browser/user_metrics.h"
 #include "content/public/common/content_features.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/feature_h264_with_openh264_ffmpeg.h"
 #include "content/public/common/features.h"
+#include "device/base/features.h"
 #include "extensions/features/features.h"
 #include "gin/public/gin_features.h"
 #include "media/audio/audio_features.h"
 #include "media/base/media_switches.h"
 #include "media/media_features.h"
 #include "media/midi/midi_switches.h"
 #include "net/cert/cert_verify_proc_android.h"
 #include "ppapi/features/features.h"
 #include "printing/features/features.h"
 #include "ui/base/ui_base_switches.h"
@@ skipping 2117 matching lines @@
 
 #if defined(OS_CHROMEOS)
     {"force-enable-stylus-tools", IDS_FLAGS_FORCE_ENABLE_STYLUS_TOOLS_NAME,
      IDS_FLAGS_FORCE_ENABLE_STYLUS_TOOLS_DESCRIPTION, kOsCrOS,
      SINGLE_VALUE_TYPE(ash::switches::kAshForceEnablePalette)},
 #endif // defined(OS_CHROMEOS)
 
     {"enable-midi-manager-dynamic-instantiation",
      IDS_FLAGS_ENABLE_MIDI_MANAGER_DYNAMIC_INSTANTIATION_NAME,
      IDS_FLAGS_ENABLE_MIDI_MANAGER_DYNAMIC_INSTANTIATION_DESCRIPTION, kOsAll,
-     FEATURE_VALUE_TYPE(midi::features::kMidiManagerDynamicInstantiation)}
+     FEATURE_VALUE_TYPE(midi::features::kMidiManagerDynamicInstantiation)},
+
+#if defined(OS_WIN)

[scheib, 2017/02/11 01:45:18]

Are these #if defined required? IIRC the logic of only showing the flag on the
right platforms is handled by the kOsWin flag that is passed in. I think this
may be cargo culting -- there are examples of other kOsAndroid that don't need
the guards.

[Reilly Grant (use Gerrit), 2017/02/11 01:48:55]

The base::Feature instance is defined within #if guards so I can't refer to it
here without them.

+    {"new-usb-backend", IDS_FLAGS_NEW_USB_BACKEND_NAME,
+     IDS_FLAGS_NEW_USB_BACKEND_DESCRIPTION, kOsWin,
+     FEATURE_VALUE_TYPE(device::kNewUsbBackend)},
+#endif  // defined(OS_WIN)
 
     // NOTE: Adding new command-line switches requires adding corresponding
     // entries to enum "LoginCustomFlags" in histograms.xml. See note in
     // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.
 };
 
 class FlagsStateSingleton {
  public:
   FlagsStateSingleton()
       : flags_state_(kFeatureEntries, arraysize(kFeatureEntries)) {}
@@ skipping 189 matching lines @@
 const base::HistogramBase::Sample kBadSwitchFormatHistogramId = 0;
 
 const FeatureEntry* GetFeatureEntries(size_t* count) {
   *count = arraysize(kFeatureEntries);
   return kFeatureEntries;
 }
 
 }  // namespace testing
 
 }  // namespace about_flags