Take 2 at browser_sync::ExtensionsActivityMonitor....

chrome/browser/sync/util/extensions_activity_monitor.cc

 // Copyright (c) 2009 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/sync/util/extensions_activity_monitor.h"
 
 #include "base/task.h"
 #include "chrome/browser/chrome_thread.h"
 #include "chrome/browser/extensions/extension_bookmarks_module.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/notification_service.h"
 
 namespace browser_sync {
 
 namespace {
 // A helper task to register an ExtensionsActivityMonitor as an observer of
 // events on the UI thread (even though the monitor may live on another thread).
 // This liberates ExtensionsActivityMonitor from having to be ref counted.
 class RegistrationTask : public Task {
  public:
   RegistrationTask(ExtensionsActivityMonitor* monitor,
-                   MessageLoop* ui_loop,
                    NotificationRegistrar* registrar)
-      : monitor_(monitor), ui_loop_(ui_loop), registrar_(registrar) {}
+      : monitor_(monitor), registrar_(registrar) {}
   virtual ~RegistrationTask() {}
 
   virtual void Run() {
-    DCHECK_EQ(MessageLoop::current(),
-              ChromeThread::GetMessageLoop(ChromeThread::UI));
+    DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
 
     // It would be nice if we could specify a Source for each specific function
     // we wanted to observe, but the actual function objects are allocated on
     // the fly so there is no reliable object to point to (same problem if we
     // wanted to use the string name).  Thus, we use all sources and filter in
     // Observe.
     registrar_->Add(monitor_, NotificationType::EXTENSION_BOOKMARKS_API_INVOKED,
                     NotificationService::AllSources());
   }
 
  private:
   ExtensionsActivityMonitor* monitor_;
-  MessageLoop* const ui_loop_;
   NotificationRegistrar* registrar_;
   DISALLOW_COPY_AND_ASSIGN(RegistrationTask);
 };
 }  // namespace
 
-ExtensionsActivityMonitor::ExtensionsActivityMonitor(MessageLoop* ui_loop)
-    : ui_loop_(ui_loop) {
-  ui_loop_->PostTask(FROM_HERE, new RegistrationTask(this, ui_loop,
-                                                     &registrar_));
+ExtensionsActivityMonitor::ExtensionsActivityMonitor() {
+  ChromeThread::PostTask(ChromeThread::UI, FROM_HERE,
+                         new RegistrationTask(this, &registrar_));
 }
 
 ExtensionsActivityMonitor::~ExtensionsActivityMonitor() {
-  DCHECK_EQ(MessageLoop::current(), ui_loop_);
-  // The registrar calls RemoveAll in its dtor (which would happen in a moment)
-  // but explicitly call this so it is clear why we need to be on the ui_loop_.
-  registrar_.RemoveAll();
+  // In some unrelated unit tests, there is no running UI loop.  In this case,
+  // the PostTask in our ctor will not result in anything running, so |this|
+  // won't be used for anything. In this case (or whenever no registration took
+  // place) and only this case we allow destruction on another loop, but this
+  // isn't something a client of this class can control; it happens implicitly
+  // by not having a running UI thread.
+  if (!registrar_.IsEmpty()) {
+    DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
+
+    // The registrar calls RemoveAll in its dtor (which would happen in a
+    // moment but explicitly call this so it is clear why we need to be on the
+    // ui_loop_.
+    registrar_.RemoveAll();
+  }
 }
 
 void ExtensionsActivityMonitor::GetAndClearRecords(Records* buffer) {
   AutoLock lock(records_lock_);
   buffer->clear();
   buffer->swap(records_);
 }
 
 void ExtensionsActivityMonitor::PutRecords(const Records& records) {
   AutoLock lock(records_lock_);
   for (Records::const_iterator i = records.begin(); i != records.end(); ++i) {
     records_[i->first].extension_id = i->second.extension_id;
     records_[i->first].bookmark_write_count += i->second.bookmark_write_count;
   }
 }
 
 void ExtensionsActivityMonitor::Observe(NotificationType type,
                                         const NotificationSource& source,
                                         const NotificationDetails& details) {
   AutoLock lock(records_lock_);
-  DCHECK_EQ(MessageLoop::current(), ui_loop_);
+  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
   const Extension* extension = Source<const Extension>(source).ptr();
   const BookmarksFunction* f = Details<const BookmarksFunction>(details).ptr();
   if (f->name() == "bookmarks.update" ||
       f->name() == "bookmarks.move" ||
       f->name() == "bookmarks.create" ||
       f->name() == "bookmarks.removeTree" ||
       f->name() == "bookmarks.remove") {
     Record& record = records_[extension->id()];
     record.extension_id = extension->id();
     record.bookmark_write_count++;
   }
 }
 
 }  // namespace browser_sync