Add a method to tab_utils.h to find out whether a tab is playing audio.

chrome/browser/media/audio_stream_indicator.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/media/audio_stream_indicator.h"
+
+#include "base/bind.h"
+#include "chrome/browser/tab_contents/tab_util.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/invalidate_type.h"
+#include "content/public/browser/render_process_host.h"
+#include "content/public/browser/render_view_host.h"
+#include "content/public/browser/web_contents.h"
+
+using content::BrowserThread;
+using content::WebContents;
+
+AudioStreamIndicator::AudioStreamIndicator() {}
+AudioStreamIndicator::~AudioStreamIndicator() {}
+
+void AudioStreamIndicator::UpdateWebContentsStatus(int render_process_id,
+                                                   int render_view_id,
+                                                   int stream_id,
+                                                   bool playing) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  BrowserThread::PostTask(
+      BrowserThread::UI, FROM_HERE,
+      base::Bind(&AudioStreamIndicator::UpdateWebContentsStatusOnUIThread,
+                 this, render_process_id, render_view_id, stream_id, playing));
+}
+
+bool AudioStreamIndicator::IsPlayingAudio(WebContents* contents) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  RenderViewId id(contents->GetRenderProcessHost()->GetID(),
+                  contents->GetRenderViewHost()->GetRoutingID());
+  return audio_streams_.find(id) != audio_streams_.end();
+}
+
+AudioStreamIndicator::RenderViewId::RenderViewId(int render_process_id,
+                                                 int render_view_id)
+    : render_process_id(render_process_id),
+      render_view_id(render_view_id) {
+}
+
+bool AudioStreamIndicator::RenderViewId::operator<(
+    const RenderViewId& other) const {
+  if (render_process_id != other.render_process_id)
+    return render_process_id < other.render_process_id;
+
+  return render_view_id < other.render_view_id;
+}
+
+void AudioStreamIndicator::UpdateWebContentsStatusOnUIThread(
+    int render_process_id,
+    int render_view_id,
+    int stream_id,
+    bool playing) {
+  RenderViewId id(render_process_id, render_view_id);

[miu, 2013/02/11 20:51:47]

nit: Can you add the following to the top of this method?

  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));

[Bernhard Bauer, 2013/02/12 18:06:27]

Done.

+  if (playing) {
+    audio_streams_[id].insert(stream_id);
+  } else {
+    std::map<RenderViewId, std::set<int> >::iterator it =
+        audio_streams_.find(id);
+    if (it != audio_streams_.end())
+      return;
+
+    it->second.erase(stream_id);
+    if (it->second.empty())
+      audio_streams_.erase(it);
+  }
+
+  WebContents* web_contents = tab_util::GetWebContentsByID(render_process_id,
+                                                           render_view_id);
+  if (web_contents)
+    web_contents->NotifyNavigationStateChanged(content::INVALIDATE_TYPE_TAB);
+}