Make tab audible and muted states and cause available for an extension API

chrome/browser/ui/tabs/tab_utils.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/ui/tabs/tab_utils.h"
 
 #include "base/command_line.h"
 #include "base/strings/string16.h"
 #include "chrome/browser/media/media_capture_devices_dispatcher.h"
 #include "chrome/browser/media/media_stream_capture_indicator.h"
@@ skipping 234 matching lines @@
     case TAB_MEDIA_STATE_AUDIO_MUTING:
       return IsTabAudioMutingFeatureEnabled();
     case TAB_MEDIA_STATE_RECORDING:
     case TAB_MEDIA_STATE_CAPTURING:
       return false;
   }
   NOTREACHED();
   return false;
 }
 
-void SetTabAudioMuted(content::WebContents* contents, bool mute) {
+void SetTabAudioMuted(content::WebContents* contents,
+                      bool muted,
+                      const std::string& cause) {
   if (!contents || !chrome::CanToggleAudioMute(contents))
     return;
-  contents->SetAudioMuted(mute);
+  contents->SetAudioMuted(muted, cause);

[miu, 2015/01/16 23:04:12]

Following up on what jam said:
I think you could add a WebContentsUserData class here (in tab_utils.cc) to
store the "cause" string, and this would allow you to easily remove it from all
the src/content APIs and code:

  struct LastMuteMetadata : public
content::WebContentsUserData<LastMuteMetadata> {
    string cause;  // Extension ID or constant from header file or empty string
  
   private:
    explicit LastMuteMetadata(content::WebContents* contents) {}
    friend struct content::WebContentsUserData<LastMuteMetadata>;
  };
  
  DEFINE_WEB_CONTENTS_USER_DATA_KEY(LastMuteMetadata);

...then, in SetTabAudioMuted(), just before the content->SetAudioMuted() call:

  LastMuteMetadata::CreateForWebContents(contents);  // Create if not exists.
  LastMuteMetadata::FromWebContents(contents)->cause = cause;

...then, you can also add the GetTabAudioMutedCause() function here in
tab_utils.cc:

  const char kMutedToggleCauseCapture[] = "auto-forced for capture";

  const std::string& GetTabAudioMutedCause(content::WebContents* contents) {
    LastMuteMetadata::CreateForWebContents(contents);  // Create if not exists.
    if (GetTabMediaStateForContents(contents) == TAB_MEDIA_STATE_CAPTURING) {
      // For tab capture, libcontent forces muting off.
      LastMuteMetadata::FromWebContents(contents)->cause =
kMutedToggleCauseCapture;
    }
    return LastMuteMetadata::FromWebContents(contents)->cause;
  }

 }
 
 bool IsTabAudioMuted(content::WebContents* contents) {
   return contents && contents->IsAudioMuted();
 }
 
 bool AreAllTabsMuted(const TabStripModel& tab_strip,
                      const std::vector<int>& indices) {
   for (std::vector<int>::const_iterator i = indices.begin(); i != indices.end();
        ++i) {
     if (!IsTabAudioMuted(tab_strip.GetWebContentsAt(*i)))
       return false;
   }
   return true;
 }
 
 }  // namespace chrome