fix browser crash when closing 2 or more tabs running getUserMedia

chrome/browser/media/media_stream_capture_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/media_stream_capture_indicator.h"
 
 #include "base/bind.h"
 #include "base/i18n/rtl.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/app/chrome_command_ids.h"
@@ skipping 405 matching lines @@
   UpdateStatusTrayIconContextMenu();
 
   ShowBalloon(render_process_id, render_view_id, audio, video);
 }
 
 void MediaStreamCaptureIndicator::RemoveCaptureDeviceTab(
     int render_process_id,
     int render_view_id,
     const content::MediaStreamDevices& devices) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
   CaptureDeviceTabs::iterator iter = std::find_if(
       tabs_.begin(), tabs_.end(), TabEquals(render_process_id, render_view_id));
-  DCHECK(iter != tabs_.end());
 
-  content::MediaStreamDevices::const_iterator dev = devices.begin();
-  for (; dev != devices.end(); ++dev) {
-    DCHECK(dev->type == content::MEDIA_STREAM_DEVICE_TYPE_AUDIO_CAPTURE ||
-           dev->type == content::MEDIA_STREAM_DEVICE_TYPE_VIDEO_CAPTURE);
-    if (dev->type == content::MEDIA_STREAM_DEVICE_TYPE_AUDIO_CAPTURE)
-      --iter->audio_ref_count;
-    else
-      --iter->video_ref_count;
+  if (iter != tabs_.end()) {

[Ami GONE FROM CHROMIUM, 2012/08/24 17:57:57]

Do you understand how it can happen that this is ==?

[no longer working on chromium, 2012/08/24 18:09:58]

Yes. This happens when we have multiple tabs using getUserMedia, and we "close
other tabs".
When tabs go away at the same time, in UpdateStatusTrayIconContextMenu, we
delete the element if we find out the tab has gone away, so the next
notification will hit this.

+    content::MediaStreamDevices::const_iterator dev = devices.begin();
+    for (; dev != devices.end(); ++dev) {
+      DCHECK(dev->type == content::MEDIA_STREAM_DEVICE_TYPE_AUDIO_CAPTURE ||
+             dev->type == content::MEDIA_STREAM_DEVICE_TYPE_VIDEO_CAPTURE);
+      if (dev->type == content::MEDIA_STREAM_DEVICE_TYPE_AUDIO_CAPTURE)
+        --iter->audio_ref_count;
+      else
+        --iter->video_ref_count;
 
-    DCHECK_GE(iter->audio_ref_count, 0);
-    DCHECK_GE(iter->video_ref_count, 0);
+      DCHECK_GE(iter->audio_ref_count, 0);
+      DCHECK_GE(iter->video_ref_count, 0);
+    }
+
+    // Remove the tab if all the devices have been closed.
+    if (iter->audio_ref_count == 0 && iter->video_ref_count == 0)
+      tabs_.erase(iter);
   }
 
-  // Remove the tab if all the devices have been closed.
-  if (iter->audio_ref_count == 0 && iter->video_ref_count == 0)
-    tabs_.erase(iter);
-
   UpdateStatusTrayIconContextMenu();

[Ami GONE FROM CHROMIUM, 2012/08/24 17:57:57]

Do you want to do this even if iter==tabs_.end() (and thus no other work has
been done)?
If not, can replace the != with a == and early-return, and de-indent l.430-445.

[no longer working on chromium, 2012/08/24 18:09:58]

Good question, I think both ways work the same. But I did it this way since I
felt it was safer to call  UpdateStatusTrayIconContextMenu here.
But I am quite OK to switch to another if you think it is better.

[Ami GONE FROM CHROMIUM, 2012/08/24 18:21:41]

I don't know the code to make a call.  It's up to you.

 }
 
 void MediaStreamCaptureIndicator::EnsureImageLoadingTracker() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   if (tracker_.get())
     return;
 
   tracker_.reset(new ImageLoadingTracker(this));
   pending_messages_.clear();
   request_index_ = 0;
 }