Run Chrome OS accessibility histograms on main thread.

content/browser/accessibility/browser_accessibility_state_impl_win.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 <psapi.h>
 #include <windows.h>
 
 #include "base/file_path.h"
 #include "base/metrics/histogram.h"
 #include "base/string_util.h"
 
 namespace content {
 
 void BrowserAccessibilityStateImpl::UpdatePlatformSpecificHistograms() {
+  // NOTE: this method is run from the file thread to reduce jank, since
+  // there's no guarantee these system calls will return quickly. Be careful
+  // not to add any code that isn't safe to run from a non-main thread!
+
   AUDIODESCRIPTION audio_description = {0};
   audio_description.cbSize = sizeof(AUDIODESCRIPTION);
   SystemParametersInfo(SPI_GETAUDIODESCRIPTION, 0, &audio_description, 0);
   UMA_HISTOGRAM_BOOLEAN("Accessibility.WinAudioDescription",
                         !!audio_description.Enabled);
 
   BOOL win_screen_reader = FALSE;
   SystemParametersInfo(SPI_GETSCREENREADER, 0, &win_screen_reader, 0);
   UMA_HISTOGRAM_BOOLEAN("Accessibility.WinScreenReader",
                         !!win_screen_reader);
@@ skipping 37 matching lines @@
       zoomtext = true;
   }
 
   UMA_HISTOGRAM_BOOLEAN("Accessibility.WinJAWS", jaws);
   UMA_HISTOGRAM_BOOLEAN("Accessibility.WinNVDA", nvda);
   UMA_HISTOGRAM_BOOLEAN("Accessibility.WinSAToGo", satogo);
   UMA_HISTOGRAM_BOOLEAN("Accessibility.WinZoomText", zoomtext);
 }
 
 }  // namespace content