a11y: Move CreateTextMarker[Range] to TextMarkerHelperMac.

ui/accessibility/BUILD.gn

Index: ui/accessibility/BUILD.gn
diff --git a/ui/accessibility/BUILD.gn b/ui/accessibility/BUILD.gn
index 422dd09b1ca7b8c30d3eb42f4a71dc62ca07eebc..2a6974d3ce1ac68d04adb19b58e2b95573b4429f 100644
--- a/ui/accessibility/BUILD.gn
+++ b/ui/accessibility/BUILD.gn
@@ -16,6 +16,8 @@ if (is_android) {
 
 component("accessibility") {
   sources = [
+    "ax_abstract_position.cc",
+    "ax_abstract_position.h",
     "ax_action_data.cc",
     "ax_action_data.h",
     "ax_export.h",
@@ -70,6 +72,8 @@ component("accessibility") {
       "platform/ax_platform_node_mac.mm",
       "platform/ax_platform_node_win.cc",
       "platform/ax_platform_node_win.h",
+      "platform/text_marker_helper_mac.h",
+      "platform/text_marker_helper_mac.mm",
     ]
   }