Make SelectionController::SelectClosestWordOrLinkFromMouseEvent() not to use VisibleSelection

This patch changes |SelectionControlle::SelectClosestWordOrLinkFromMouseEvent()|
to use |SelectionInFlatTree| instead of |VisibleSelection| since it is
redundant, for improving code health.

This is follow-up of the patch[1].

[1] http://crrev.com/c/595309: Make ExpandSelectionToRespectUserSelectAll() to
take SelectionInFlatTree

Bug: 657237
Change-Id: I4fb3c71c27f3b32322311724a99a44f61376b5ec
Reviewed-on: https://chromium-review.googlesource.com/597091Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491330}

third_party/WebKit/Source/core/editing/SelectionController.cpp

@@ -667,18 +667,17 @@ void SelectionController::SelectClosestWordOrLinkFromMouseEvent(
   Element* url_element = result.GetHitTestResult().URLElement();
   const VisiblePositionInFlatTree pos =
       VisiblePositionOfHitTestResult(result.GetHitTestResult());
-  const VisibleSelectionInFlatTree& new_selection =
+  const SelectionInFlatTree& new_selection =
       pos.IsNotNull() &&
               pos.DeepEquivalent().AnchorNode()->IsDescendantOf(url_element)
-          ? CreateVisibleSelection(SelectionInFlatTree::Builder()
-                                       .SelectAllChildren(*url_element)
-                                       .Build())
-          : VisibleSelectionInFlatTree();
+          ? SelectionInFlatTree::Builder()
+                .SelectAllChildren(*url_element)
+                .Build()
+          : SelectionInFlatTree();
 
   UpdateSelectionForMouseDownDispatchingSelectStart(
       inner_node,
-      ExpandSelectionToRespectUserSelectAll(inner_node,
-                                            new_selection.AsSelection()),
+      ExpandSelectionToRespectUserSelectAll(inner_node, new_selection),
       TextGranularity::kWord, HandleVisibility::kNotVisible);
 }