Move ui::GetAtom to gfx::GetAtom

This CL is a followup to [1].  However, unlike that CL, this one
should have no functional changes as it is purely a refactoring.

This CL adds gfx::GetAtom (and renames the ::ui namespace in
x11_atom_cache to ::gfx) and updates all references that used to point
to ui::GetAtom to gfx::GetAtom.

Also update PRESUBMIT.py to include exceptions for 2 files that use
XInternAtom appropriately.

[1] https://codereview.chromium.org/2914103002/

BUG=730889
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[email protected]

Review-Url: https://codereview.chromium.org/2924343002
Cr-Commit-Position: refs/heads/master@{#478103}
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index c0324ab8..46e16be0 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -191,11 +191,12 @@
     (
       r'XInternAtom|xcb_intern_atom',
       (
-       'Use ui::GetAtom() or ui::X11AtomCache::GetAtom() instead of',
-       'interning atoms directly.',
+       'Use gfx::GetAtom() instead of interning atoms directly.',
       ),
       True,
       (
+        r"^gpu[\\\/]ipc[\\\/]service[\\\/]gpu_watchdog_thread\.cc$",
+        r"^remoting[\\\/]host[\\\/]linux[\\\/]x_server_clipboard\.cc$",
         r"^ui[\\\/]gfx[\\\/]x[\\\/]x11_atom_cache\.cc$",
       ),
     ),