cros: Remove some OS platform ifdefs from ash

ash/wm/ash_native_cursor_manager.cc

Index: ash/wm/ash_native_cursor_manager.cc
diff --git a/ash/wm/ash_native_cursor_manager.cc b/ash/wm/ash_native_cursor_manager.cc
index 3ab68949ae54694ca3cf05bd71fc85bbc27998b2..d79bd5d0af84cb54b780dc2404d4d776b3b381f5 100644
--- a/ash/wm/ash_native_cursor_manager.cc
+++ b/ash/wm/ash_native_cursor_manager.cc
@@ -24,12 +24,11 @@ void SetCursorOnAllRootWindows(gfx::NativeCursor cursor) {
   for (aura::Window::Windows::iterator iter = root_windows.begin();
        iter != root_windows.end(); ++iter)
     (*iter)->GetHost()->SetCursor(cursor);
-#if defined(OS_CHROMEOS)
+
   Shell::GetInstance()
       ->window_tree_host_manager()
       ->cursor_window_controller()
       ->SetCursor(cursor);
-#endif
 }
 
 void NotifyCursorVisibilityChange(bool visible) {
@@ -38,12 +37,11 @@ void NotifyCursorVisibilityChange(bool visible) {
   for (aura::Window::Windows::iterator iter = root_windows.begin();
        iter != root_windows.end(); ++iter)
     (*iter)->GetHost()->OnCursorVisibilityChanged(visible);
-#if defined(OS_CHROMEOS)
+
   Shell::GetInstance()
       ->window_tree_host_manager()
       ->cursor_window_controller()
       ->SetVisibility(visible);
-#endif
 }
 
 void NotifyMouseEventsEnableStateChange(bool enabled) {
@@ -79,22 +77,17 @@ void AshNativeCursorManager::SetDisplay(
                                    ->display_manager()
                                    ->GetDisplayInfo(display.id())
                                    .device_scale_factor();
-#if defined(OS_CHROMEOS)
   // And use the nearest resource scale factor.
   const float cursor_scale =
       ui::GetScaleForScaleFactor(ui::GetSupportedScaleFactor(original_scale));
-#else
-  // TODO(oshima): crbug.com/143619
-  const float cursor_scale = original_scale;
-#endif
+
   if (image_cursors_->SetDisplay(display, cursor_scale))
     SetCursor(delegate->GetCursor(), delegate);
-#if defined(OS_CHROMEOS)
+
   Shell::GetInstance()
       ->window_tree_host_manager()
       ->cursor_window_controller()
       ->SetDisplay(display);
-#endif
 }
 
 void AshNativeCursorManager::SetCursor(
@@ -131,12 +124,10 @@ void AshNativeCursorManager::SetCursorSet(
   if (delegate->IsCursorVisible())
     SetCursor(delegate->GetCursor(), delegate);
 
-#if defined(OS_CHROMEOS)
   Shell::GetInstance()
       ->window_tree_host_manager()
       ->cursor_window_controller()
       ->SetCursorSet(cursor_set);
-#endif
 }
 
 void AshNativeCursorManager::SetVisibility(