views: support vertical-drag-to-end on textfields

ui/views/controls/textfield/textfield.cc

Index: ui/views/controls/textfield/textfield.cc
diff --git a/ui/views/controls/textfield/textfield.cc b/ui/views/controls/textfield/textfield.cc
index 74d18b70564e2ea7e60de96e11fb9c83c41cfb45..dc9dd455a452c92dd31e516be6963b04fee96770 100644
--- a/ui/views/controls/textfield/textfield.cc
+++ b/ui/views/controls/textfield/textfield.cc
@@ -40,6 +40,7 @@
 #include "ui/views/metrics.h"
 #include "ui/views/native_cursor.h"
 #include "ui/views/painter.h"
+#include "ui/views/style/platform_style.h"
 #include "ui/views/views_delegate.h"
 #include "ui/views/widget/widget.h"
 
@@ -1746,7 +1747,15 @@ void Textfield::MoveCursorTo(const gfx::Point& point, bool select) {
 
 void Textfield::SelectThroughLastDragLocation() {
   OnBeforeUserAction();
-  model_->MoveCursorTo(last_drag_location_, true);
+
+  const bool drags_to_end = PlatformStyle::kTextfieldDragVerticallyDragsToEnd;
+  if (drags_to_end && last_drag_location_.y() < 0)
+    model_->MoveCursorToStart(true);
+  else if (drags_to_end && last_drag_location_.y() > height())
+    model_->MoveCursorToEnd(true);
+  else
+    model_->MoveCursorTo(last_drag_location_, true);
+
   if (aggregated_clicks_ == 1) {
     model_->SelectWord();
     // Expand the selection so the initially selected word remains selected.