Use in screen pixel conversion for touch exploration

- Touch events come in screen pixel. We need to use in screen pixel
  conversion here as the comment in the file says.

  that touch exploration works correctly on the touch controller.

Bug: 887222
Test: Enable spoken feedback on touch controller of CfM unit. Confirm
Change-Id: Ic7a83eb5d9c4690b41a184ab85d5421e0468934e
Reviewed-on: https://chromium-review.googlesource.com/1235489
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592777}

ash/accessibility/touch_exploration_controller.cc

@@ -107,8 +107,8 @@ ui::EventRewriteStatus TouchExplorationController::RewriteEvent(
   // is what the rest of this class expects.
   gfx::Point location = touch_event.location();
   gfx::Point root_location = touch_event.root_location();
-  root_window_->GetHost()->ConvertPixelsToDIP(&location);
-  root_window_->GetHost()->ConvertPixelsToDIP(&root_location);
+  root_window_->GetHost()->ConvertScreenInPixelsToDIP(&location);
+  root_window_->GetHost()->ConvertScreenInPixelsToDIP(&root_location);
 
   if (!exclude_bounds_.IsEmpty()) {
     bool in_exclude_area = exclude_bounds_.Contains(location);