Utilize EphemeralRange::IsCollapsed() in ComputeAdjustedSelection()

This patch makes |ComputeAdjustedSelection()| to utilize |IsCollapsed()|
of |EphemeralRange|[1] to simplify source code for improving code health.

Note: This patch doesn't change behavior.

[1] http://crrev.com/c/2550834: [editing] Ranges with equivalent positions
should be collapsed

Change-Id: Iab464fafb0f02f90d346bc1cbc0a2734d6744138
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2567146
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832722}

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

@@ -43,10 +43,9 @@ template <typename Strategy>
 SelectionTemplate<Strategy> ComputeAdjustedSelection(
     const SelectionTemplate<Strategy> selection,
     const EphemeralRangeTemplate<Strategy>& range) {
-  if (range.StartPosition().CompareTo(range.EndPosition()) == 0) {
+  if (range.IsCollapsed()) {
     return typename SelectionTemplate<Strategy>::Builder()
-        .Collapse(selection.IsBaseFirst() ? range.StartPosition()
-                                          : range.EndPosition())
+        .Collapse(range.StartPosition())
         .Build();
   }
   if (selection.IsBaseFirst()) {