Fix use after free for cached_displays_.

ui/display/manager/chromeos/display_change_observer.cc

 // Copyright 2013 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 "ui/display/manager/chromeos/display_change_observer.h"
 
 #include <algorithm>
 #include <map>
 #include <set>
 #include <string>
@@ skipping 270 matching lines @@
     const ui::DisplayConfigurator::DisplayStateList& displays,
     ui::MultipleDisplayState failed_new_state) {
   // If display configuration failed during startup, simply update the display
   // manager with detected displays. If no display is detected, it will
   // create a pseudo display.
   if (display_manager_->GetNumDisplays() == 0)
     OnDisplayModeChanged(displays);
 }
 
 void DisplayChangeObserver::OnTouchscreenDeviceConfigurationChanged() {
-  OnDisplayModeChanged(display_configurator_->cached_displays());
+  // If there are no cached display snapshots, either there are no attached
+  // displays or the cached snapshots have been invalidated. For the first case
+  // there aren't any touchscreens to associate. For the second case, the
+  // displays and touch input-devices will get associated when display
+  // configuration finishes.
+  const auto& cached_displays = display_configurator_->cached_displays();
+  if (!cached_displays.empty())
+    OnDisplayModeChanged(cached_displays);
+  else
+    VLOG(1) << "Not updating touchscreen associations";
 }
 
 // static
 float DisplayChangeObserver::FindDeviceScaleFactor(float dpi) {
   for (size_t i = 0; i < arraysize(kThresholdTable); ++i) {
     if (dpi > kThresholdTable[i].dpi)
       return kThresholdTable[i].device_scale_factor;
   }
   return 1.0f;
 }
 
 }  // namespace display