Run Chrome OS accessibility histograms on main thread.

content/browser/accessibility/browser_accessibility_state_impl_win.cc

Index: content/browser/accessibility/browser_accessibility_state_impl_win.cc
diff --git a/content/browser/accessibility/browser_accessibility_state_impl_win.cc b/content/browser/accessibility/browser_accessibility_state_impl_win.cc
index d17a3966af6d4923eb11a8b0ca2b54b912909a44..f65e0efe068495a69243be005bf9b12bb7e7ba2e 100644
--- a/content/browser/accessibility/browser_accessibility_state_impl_win.cc
+++ b/content/browser/accessibility/browser_accessibility_state_impl_win.cc
@@ -14,6 +14,10 @@
 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);