Make //ui/base/cursor:theme_manager a component

CursorThemeManager is a singleton and, because its source_set is
depended upon by different targets, its static instance was not being
shared.

Bug: 1114812
Change-Id: Iaaa0a6fee05ff5f5504c8320072f0710d3315e8c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2367096Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Cr-Commit-Position: refs/heads/master@{#803683}

ui/base/cursor/BUILD.gn

@@ -33,12 +33,14 @@ component("cursor_base") {
   }
 }
 
-source_set("theme_manager") {
+component("theme_manager") {
+  output_name = "ui_base_cursor_theme_manager"
   sources = [
     "cursor_theme_manager.cc",
     "cursor_theme_manager.h",
     "cursor_theme_manager_observer.h",
   ]
+  defines = [ "IS_UI_BASE_CURSOR_THEME_MANAGER_IMPL" ]
   deps = [ "//base" ]
 }
 

ui/base/cursor/cursor_theme_manager.h

@@ -7,12 +7,13 @@
 
 #include <string>
 
+#include "base/component_export.h"
 #include "base/observer_list.h"
 #include "ui/base/cursor/cursor_theme_manager_observer.h"
 
 namespace ui {
 
-class CursorThemeManager {
+class COMPONENT_EXPORT(UI_BASE_CURSOR_THEME_MANAGER) CursorThemeManager {
  public:
   CursorThemeManager(const CursorThemeManager&) = delete;
   CursorThemeManager& operator=(const CursorThemeManager&) = delete;