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

chrome/browser/ui/tabs/tab_utils.cc

Index: chrome/browser/ui/tabs/tab_utils.cc
diff --git a/chrome/browser/ui/tabs/tab_utils.cc b/chrome/browser/ui/tabs/tab_utils.cc
index a61996701309b28c8d94d985247a30ef396d64ae..f1d7035b7caf747bf6c38035d1e2b1c373d157a1 100644
--- a/chrome/browser/ui/tabs/tab_utils.cc
+++ b/chrome/browser/ui/tabs/tab_utils.cc
@@ -252,10 +252,12 @@ bool CanToggleAudioMute(content::WebContents* contents) {
   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) {