Reland: Implement Aura side of unified touch text selection for contents

ui/touch_selection/BUILD.gn

Index: ui/touch_selection/BUILD.gn
diff --git a/ui/touch_selection/BUILD.gn b/ui/touch_selection/BUILD.gn
index b1d9535a8f6426b6a59d448bd3538467753e5b21..ee257e81f27bcc752cd023cb4abdd4f3f26e9884 100644
--- a/ui/touch_selection/BUILD.gn
+++ b/ui/touch_selection/BUILD.gn
@@ -53,6 +53,19 @@ component("touch_selection") {
   }
 }
 
+static_library("test_support") {
+  testonly = true
+
+  sources = [
+    "touch_selection_controller_test_api.cc",
+    "touch_selection_controller_test_api.h",
+  ]
+
+  deps = [
+    ":touch_selection",
+  ]
+}
+
 test("ui_touch_selection_unittests") {
   sources = [
     "longpress_drag_selector_unittest.cc",
@@ -61,6 +74,7 @@ test("ui_touch_selection_unittests") {
   ]
 
   deps = [
+    ":test_support",
     ":touch_selection",
     "//base/test:run_all_unittests",
     "//testing/gmock:gmock",