Support longpress drag selection

ui/touch_selection/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 component("touch_selection") {
   output_name = "ui_touch_selection"
 
   sources = [
+    "longpress_drag_selector.cc",
+    "longpress_drag_selector.h",
     "selection_event_type.h",
     "touch_handle.cc",
     "touch_handle.h",
     "touch_handle_drawable_aura.cc",
     "touch_handle_drawable_aura.h",
     "touch_handle_orientation.h",
     "touch_selection_controller.cc",
     "touch_selection_controller.h",
+    "touch_selection_draggable.h",
     "ui_touch_selection_export.h",
   ]
 
   defines = [ "UI_TOUCH_SELECTION_IMPLEMENTATION" ]
 
   deps = [
     "//skia:skia",
     "//base:base",
     "//ui/aura:aura",
     "//ui/aura_extra:aura_extra",
@@ skipping 16 matching lines @@
 
     sources -= [
       "touch_handle_drawable_aura.cc",
       "touch_handle_drawable_aura.h",
     ]
   }
 }
 
 test("ui_touch_selection_unittests") {
   sources = [
+    "longpress_drag_selector_unittest.cc",
     "touch_handle_unittest.cc",
     "touch_selection_controller_unittest.cc",
   ]
 
   deps = [
     ":touch_selection",
     "//base/test:run_all_unittests",
     "//testing/gmock:gmock",
     "//testing/gtest:gtest",
     "//ui/base:base",
@@ skipping 14 matching lines @@
   }
   java_cpp_enum("ui_touch_handle_orientation_srcjar") {
     sources = [
       "touch_handle_orientation.h",
     ]
     outputs = [
       "org/chromium/ui/touch_selection/TouchHandleOrientation.java",
     ]
   }
 }