Enable MSVC warning for unused locals.

media/audio/win/audio_low_latency_input_win.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 "media/audio/win/audio_low_latency_input_win.h"
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/utf_string_conversions.h"
 #include "media/audio/win/audio_manager_win.h"
@@ skipping 222 matching lines @@
   DCHECK(CalledOnValidThread());
   DCHECK_GE(volume, 0.0);
   DCHECK_LE(volume, 1.0);
 
   DLOG_IF(ERROR, !opened_) << "Open() has not been called successfully";
   if (!opened_)
     return;
 
   // Set a new master volume level. Valid volume levels are in the range
   // 0.0 to 1.0. Ignore volume-change events.
-  HRESULT hr = simple_audio_volume_->SetMasterVolume(static_cast<float>(volume),
-      NULL);
-  DLOG_IF(WARNING, FAILED(hr)) << "Failed to set new input master volume.";
+  HRESULT hr =
+      simple_audio_volume_->SetMasterVolume(static_cast<float>(volume), NULL);
+  if (FAILED(hr))
+    DLOG(WARNING) << "Failed to set new input master volume.";

[Peter Kasting, 2014/11/18 02:17:15]

Note: There was nothing wrong with the old code except that in release mode,
|hr| appeared to be unused.  This is one possible fix; another is to add
"ALLOW_UNUSED_LOCAL(hr);" instead in these places; still another would be to do
something akin to:

#if DLOG_IS_ON
  HRESULT hr =
#endif
      ...;
  DLOG_IF...

I thought this was the least ugly choice of the three.

[wolenetz, 2014/11/20 22:47:26]

Per chat, I would prefer instead DLOG_IF implicitly referenced the condition (on
MSVC), to prevent this warning on release mode, and to prevent DLOG_IF users
from explicitly referencing the condition. 

note: I'm fine with this immediate change followed later by a revert along with
a DLOG_IF implementation update to do the implicit referencing. (Also, please
include henrika@chromium.org on that revert CR, because I'm not sure that the
previous code really should proceed here to UpdateAgcVolume() if FAILED(hr).)

[henrika (OOO until Aug 14), 2014/11/21 09:35:09]

Thanks for fixing Peter ;-)

wolenetz@: I agree that it would probably be "more correct" to avoid calling
UpdateAgcVolume()but it will actually not hurt to keep going either. If Set
fails, the Update call will do nothing and we are fine.

To keep things simple, I propose that we don't change the call-flow at this
stage if that is OK with you guys.

 
   // Update the AGC volume level based on the last setting above. Note that,
   // the volume-level resolution is not infinite and it is therefore not
   // possible to assume that the volume provided as input parameter can be
   // used directly. Instead, a new query to the audio hardware is required.
   // This method does nothing if AGC is disabled.
   UpdateAgcVolume();
 }
 
 double WASAPIAudioInputStream::GetVolume() {
   DCHECK(opened_) << "Open() has not been called successfully";
   if (!opened_)
     return 0.0;
 
   // Retrieve the current volume level. The value is in the range 0.0 to 1.0.
   float level = 0.0f;
   HRESULT hr = simple_audio_volume_->GetMasterVolume(&level);
-  DLOG_IF(WARNING, FAILED(hr)) << "Failed to get input master volume.";
+  if (FAILED(hr))
+    DLOG(WARNING) << "Failed to get input master volume.";
 
   return static_cast<double>(level);
 }
 
 bool WASAPIAudioInputStream::IsMuted() {
   DCHECK(opened_) << "Open() has not been called successfully";
   DCHECK(CalledOnValidThread());
   if (!opened_)
     return false;
 
   // Retrieves the current muting state for the audio session.
   BOOL is_muted = FALSE;
   HRESULT hr = simple_audio_volume_->GetMute(&is_muted);
-  DLOG_IF(WARNING, FAILED(hr)) << "Failed to get input master volume.";
+  if (FAILED(hr))
+    DLOG(WARNING) << "Failed to get input master volume.";
 
   return is_muted != FALSE;
 }
 
 // static
 AudioParameters WASAPIAudioInputStream::GetInputStreamParameters(
     const std::string& device_id) {
   int sample_rate = 48000;
   ChannelLayout channel_layout = CHANNEL_LAYOUT_STEREO;
 
@@ skipping 471 matching lines @@
     return hr;
 
   // Obtain a reference to the ISimpleAudioVolume interface which enables
   // us to control the master volume level of an audio session.
   hr = audio_client_->GetService(__uuidof(ISimpleAudioVolume),
                                  simple_audio_volume_.ReceiveVoid());
   return hr;
 }
 
 }  // namespace media