Run Chrome OS accessibility histograms on main thread.

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 "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "base/timer.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 31 matching lines @@
           switches::kDisableRendererAccessibility)) {
     accessibility_mode_ = AccessibilityModeEditableTextOnly;
   }
 #endif  // defined(OS_WIN)
 
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kForceRendererAccessibility)) {
     accessibility_mode_ = AccessibilityModeComplete;
   }
 
-  // UpdateHistogram only takes a couple of milliseconds, but run it on
-  // the FILE thread to guarantee there's no jank.
-  // And we need to AddRef() the leaky singleton so that Bind doesn't
+#if defined(OS_WIN)
+  // On Windows, UpdateHistogram 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, UpdateHistogram 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();
   BrowserThread::PostDelayedTask(
-      BrowserThread::FILE, FROM_HERE,
+      update_histogram_thread, FROM_HERE,
       base::Bind(&BrowserAccessibilityStateImpl::UpdateHistogram, this),
       base::TimeDelta::FromSeconds(kAccessibilityHistogramDelaySecs));
 }
 
 BrowserAccessibilityStateImpl::~BrowserAccessibilityStateImpl() {
 }
 
 void BrowserAccessibilityStateImpl::OnScreenReaderDetected() {
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDisableRendererAccessibility)) {
@@ skipping 38 matching lines @@
 AccessibilityMode BrowserAccessibilityStateImpl::GetAccessibilityMode() {
   return accessibility_mode_;
 }
 
 void BrowserAccessibilityStateImpl::SetAccessibilityMode(
     AccessibilityMode mode) {
   accessibility_mode_ = mode;
 }
 
 }  // namespace content