Fix DCHECK in browser_tests with VirtualDesktopHelper.

Pass this (base::RefCountedDeleteOnSequence) instead of a weakptr
to PostTaskAndReplyWithResult.

This should fix a lot of test flakiness due to a dcheck doing a
PostTaskAndReplyRelay.

Bug: 1093448
Change-Id: I7cb4621009c350a60c3769c6fb691a144c6fd5e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2346994Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796637}

chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc

@@ -65,8 +65,6 @@ class VirtualDesktopHelper
 
   void SetInitialWorkspaceRemembered(bool remembered);
 
-  base::WeakPtr<VirtualDesktopHelper> AsWeakPtr();
-
  private:
   friend class base::RefCountedDeleteOnSequence<VirtualDesktopHelper>;
   friend class base::DeleteHelper<VirtualDesktopHelper>;
@@ -136,7 +134,7 @@ void VirtualDesktopHelper::UpdateWindowDesktopId(
       FROM_HERE,
       base::BindOnce(&VirtualDesktopHelper::GetWindowDesktopIdImpl, hwnd,
                      virtual_desktop_manager_),
-      base::BindOnce(&VirtualDesktopHelper::SetWorkspace, AsWeakPtr(),
+      base::BindOnce(&VirtualDesktopHelper::SetWorkspace, this,
                      base::Passed(std::move(callback))));
 }
 
@@ -148,10 +146,6 @@ void VirtualDesktopHelper::SetInitialWorkspaceRemembered(bool remembered) {
   initial_workspace_remembered_ = remembered;
 }
 
-base::WeakPtr<VirtualDesktopHelper> VirtualDesktopHelper::AsWeakPtr() {
-  return weak_factory_.GetWeakPtr();
-}
-
 void VirtualDesktopHelper::SetWorkspace(WorkspaceChangedCallback callback,
                                         const std::string& workspace) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));