Revert of Switch BrowserAccessibilityStateImpl to the TaskScheduler API.

content/browser/accessibility/browser_accessibility_state_impl.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 "content/browser/accessibility/browser_accessibility_state_impl.h"
 
 #include <stddef.h>
 
 #include "base/command_line.h"
 #include "base/metrics/histogram_macros.h"
-#include "base/task_scheduler/post_task.h"
 #include "build/build_config.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/content_switches.h"
 #include "ui/gfx/color_utils.h"
 
 namespace content {
 
 // IMPORTANT!
@@ skipping 29 matching lines @@
 BrowserAccessibilityStateImpl* BrowserAccessibilityStateImpl::GetInstance() {
   return base::Singleton<
       BrowserAccessibilityStateImpl,
       base::LeakySingletonTraits<BrowserAccessibilityStateImpl>>::get();
 }
 
 BrowserAccessibilityStateImpl::BrowserAccessibilityStateImpl()
     : BrowserAccessibilityState(),
       disable_hot_tracking_(false) {
   ResetAccessibilityModeValue();
+#if defined(OS_WIN)
+  // On Windows, UpdateHistograms calls some system functions with unknown
+  // runtime, so call it on the file thread to ensure there's no jank.
+  // Everything in that method must be safe to call on another thread.
+  BrowserThread::ID update_histogram_thread = BrowserThread::FILE;
+#else
+  // On all other platforms, UpdateHistograms should be called on the main
+  // thread.
+  BrowserThread::ID update_histogram_thread = BrowserThread::UI;
+#endif
 
   // We need to AddRef() the leaky singleton so that Bind doesn't
   // delete it prematurely.
   AddRef();
-  // The delay is necessary because assistive technology sometimes isn't
-  // detected until after the user interacts in some way, so a reasonable delay
-  // gives us better numbers.
-  base::PostDelayedTaskWithTraits(
-      FROM_HERE, {base::MayBlock(), base::TaskPriority::BACKGROUND},
+  BrowserThread::PostDelayedTask(
+      update_histogram_thread, FROM_HERE,
       base::Bind(&BrowserAccessibilityStateImpl::UpdateHistograms, this),
       base::TimeDelta::FromSeconds(ACCESSIBILITY_HISTOGRAM_DELAY_SECS));
 }
 
 BrowserAccessibilityStateImpl::~BrowserAccessibilityStateImpl() {
 }
 
 void BrowserAccessibilityStateImpl::OnScreenReaderDetected() {
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDisableRendererAccessibility)) {
@@ skipping 105 matching lines @@
       accessibility_mode_.mode() ^ (mode.mode() & accessibility_mode_.mode());
   accessibility_mode_ = raw_flags;
 
   std::vector<WebContentsImpl*> web_contents_vector =
       WebContentsImpl::GetAllWebContents();
   for (size_t i = 0; i < web_contents_vector.size(); ++i)
     web_contents_vector[i]->SetAccessibilityMode(accessibility_mode());
 }
 
 }  // namespace content