Remove ui/events/platform/x11 -> ui/base/x dependency

At the moment, //ui/events/platform/x11 has a single dependency on
//ui/base/x, which is ui::XScopedEventSelector, that actually is a X11
event-related component. This CL moves XScopedEventSelector source files
into //ui/events/x, thus getting rid of aforementioned dependency, which
prevent //ui/base/x components to depend on X11EventSource* classes
(which lives on //ui/events/platform/x11), for instance, which has been
becoming more and more common in the aura/x11 -> ozone/x11 migration,
where core X11 classes are made reusable and placed in ui/base/x to be
shared between ozone and non-ozone X11, e.g: crrev.com/c/1695008.

Bug: 789065
Test: None (no functional change)
Change-Id: I94aba04b420f6d718c41abcc93ceafaf13963173
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1712955
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Sadrul Chowdhury <[email protected]>
Commit-Queue: Nick Yamane <[email protected]>
Cr-Commit-Position: refs/heads/master@{#680313}
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 9736ebf..fe8fb86 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -523,6 +523,7 @@
       ),
       True,
       (
+        r"^ui[\\/]events[\\/]x[\\/].*\.cc$",
         r"^ui[\\/]gl[\\/].*\.cc$",
         r"^media[\\/]gpu[\\/].*\.cc$",
         r"^gpu[\\/].*\.cc$",