Convert Pass()→std::move() on Windows

chrome/browser/ui/views/status_icons/status_tray_state_changer_win.cc

 // Copyright 2014 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/ui/views/status_icons/status_tray_state_changer_win.h"
 
+#include <utility>
+
 namespace {
 
 ////////////////////////////////////////////////////////////////////////////////
 // Status Tray API
 
 // The folowing describes the interface to the undocumented Windows Exporer APIs
 // for manipulating with the status tray area.  This code should be used with
 // care as it can change with versions (even minor versions) of Windows.
 
 // ITrayNotify is an interface describing the API for manipulating the state of
@@ skipping 54 matching lines @@
   // not changing anything.
   if (notify_item->preference == PREFERENCE_SHOW_NEVER)
     return;
 
   // If we are already on the taskbar, return since nothing needs to be done.
   if (notify_item->preference == PREFERENCE_SHOW_ALWAYS)
     return;
 
   notify_item->preference = PREFERENCE_SHOW_ALWAYS;
 
-  SendNotifyItemUpdate(notify_item.Pass());
+  SendNotifyItemUpdate(std::move(notify_item));
 }
 
 STDMETHODIMP_(ULONG) StatusTrayStateChangerWin::AddRef() {
   DCHECK(CalledOnValidThread());
   return base::win::IUnknownImpl::AddRef();
 }
 
 STDMETHODIMP_(ULONG) StatusTrayStateChangerWin::Release() {
   DCHECK(CalledOnValidThread());
   return base::win::IUnknownImpl::Release();
@@ skipping 71 matching lines @@
     case INTERFACE_VERSION_LEGACY:
       if (!RegisterCallbackLegacy())
         VLOG(1) << "Unable to successfully run RegisterCallbackLegacy.";
       break;
     default:
       NOTREACHED();
   }
 
   // Adding an intermediate scoped pointer here so that |notify_item_| is reset
   // to NULL.
-  scoped_ptr<NOTIFYITEM> rv(notify_item_.release());
-  return rv.Pass();
+  scoped_ptr<NOTIFYITEM> rv(std::move(notify_item_));

[brettw, 2016/03/02 19:09:08]

This code is pretty suspicious.

With your change it's equivalent to return std::move(notify_item_) and it will
have the effect of leaving notify_item_ in an undefined state.

I think you want the release() call in there as per the old code to guarantee
the state of the old value.

[mmenke, 2016/03/02 19:13:25]

Interesting...I was told this was fine for scoped_ptrs when I bought this up on
another of dcheng's CLs:  https://codereview.chromium.org/1545233002/ (Post
#12).  If we want to avoid this, I suspect we'll have to revisit a lot of
std::move calls.

[dcheng, 2016/03/02 19:38:31]

In general, you're right: you can't depend on the state of a moved-from object.
From [lib.types.movedfrom/1]:
Unless otherwise specified, such moved-from objects shall be placed in a valid
but unspecified state.

However, std::unique_ptr *is* one of the classes where the moved-from state is
defined. From [unique.ptr/4]:
  Additionally, u can, upon request, transfer ownership to another unique
pointer u2. Upon completion of
  such a transfer, the following postconditions hold:
  — u2.p is equal to the pre-transfer u.p,
  — u.p is equal to nullptr, and
  — if the pre-transfer u.d maintained state, such state has been transferred to
u2.d.

Since we aim for compatibility with std::unique_ptr, scoped_ptr also has the
same behavior.

+  return rv;
 }
 
 bool StatusTrayStateChangerWin::RegisterCallbackWin8() {
   base::win::ScopedComPtr<ITrayNotifyWin8> tray_notify_win8;
   HRESULT hr = tray_notify_win8.QueryFrom(tray_notify_.get());
   if (FAILED(hr))
     return false;
 
   // The following two lines cause Windows Explorer to call us back with all the
   // existing tray icons and their preference.  It would also presumably notify
@@ skipping 41 matching lines @@
     HRESULT hr = tray_notify.QueryFrom(tray_notify_.get());
     if (SUCCEEDED(hr))
       tray_notify->SetPreference(notify_item.get());
   } else if (interface_version_ == INTERFACE_VERSION_WIN8) {
     base::win::ScopedComPtr<ITrayNotifyWin8> tray_notify;
     HRESULT hr = tray_notify.QueryFrom(tray_notify_.get());
     if (SUCCEEDED(hr))
       tray_notify->SetPreference(notify_item.get());
   }
 }