Stop using CreateVisiblePosition in DragCaret::SetCaretPosition

The passed-in position in DragCaret::SetCaretPosition is a hit test
result (see DragController::TryDocumentDrag), which is already a
canonical position. Hence, there's no need to canonicalize it again.

Bug: 897983
Change-Id: I58f9bff731842a4d9f7c201f95ec2af769e158d7
Reviewed-on: https://chromium-review.googlesource.com/c/1297641Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602393}

third_party/blink/renderer/core/editing/drag_caret.cc

@@ -66,7 +66,7 @@ bool DragCaret::IsContentRichlyEditable() const {
 }
 
 void DragCaret::SetCaretPosition(const PositionWithAffinity& position) {
-  position_ = CreateVisiblePosition(position).ToPositionWithAffinity();
+  position_ = position;
   Document* document = nullptr;
   if (Node* node = position_.AnchorNode()) {
     document = &node->GetDocument();