Revert of Switch BrowserAccessibilityStateImpl to the TaskScheduler API.

content/browser/accessibility/browser_accessibility_state_impl.cc

Index: content/browser/accessibility/browser_accessibility_state_impl.cc
diff --git a/content/browser/accessibility/browser_accessibility_state_impl.cc b/content/browser/accessibility/browser_accessibility_state_impl.cc
index 32e17d9f019a2ab8aafb82e47e40f780fda66148..faf6a7bd412ba3745d4e9a7a84d8965df4ccbb61 100644
--- a/content/browser/accessibility/browser_accessibility_state_impl.cc
+++ b/content/browser/accessibility/browser_accessibility_state_impl.cc
@@ -8,7 +8,6 @@
 
 #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"
@@ -58,15 +57,22 @@
     : 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));
 }