Use fake Input Device Settings with chrome://device-emulator

chrome/browser/chromeos/system/input_device_settings.h

Index: chrome/browser/chromeos/system/input_device_settings.h
diff --git a/chrome/browser/chromeos/system/input_device_settings.h b/chrome/browser/chromeos/system/input_device_settings.h
index da1945861c68b801f8bc92fc0383d4326bbc4bd7..d8e55b1369663a5fa4f0c290c0f8e93861408caa 100644
--- a/chrome/browser/chromeos/system/input_device_settings.h
+++ b/chrome/browser/chromeos/system/input_device_settings.h
@@ -165,6 +165,9 @@ class CHROMEOS_EXPORT InputDeviceSettings {
   // NULL to this method.
   static void SetSettingsForTesting(InputDeviceSettings* test_settings);
 
+  // Returns true if the current instance was passed to SetSettingsForTesting.
+  static bool DidSetSettingsForTesting();
+
   // Returns true if UI should implement enhanced keyboard support for cases
   // where other input devices like mouse are absent.
   static bool ForceKeyboardDrivenUINavigation();
@@ -179,8 +182,8 @@ class CHROMEOS_EXPORT InputDeviceSettings {
   void ToggleTouchscreen();
   void ToggleTouchpad();
 
-  // Calls |callback| asynchronously after determining if a touchpad is
-  // connected.
+  // Calls |callback|, possibly asynchronously, after determining if a touchpad
+  // is connected.
   virtual void TouchpadExists(const DeviceExistsCallback& callback) = 0;
 
   // Updates several touchpad settings at a time. Updates only settings that
@@ -204,7 +207,8 @@ class CHROMEOS_EXPORT InputDeviceSettings {
   // Turns natural scrolling on/off for all devices except wheel mice
   virtual void SetNaturalScroll(bool enabled) = 0;
 
-  // Calls |callback| asynchronously after determining if a mouse is connected.
+  // Calls |callback|, possibly asynchronously, after determining if a mouse is
+  // connected.
   virtual void MouseExists(const DeviceExistsCallback& callback) = 0;
 
   // Updates several mouse settings at a time. Updates only settings that