Stop ExpandRange/EndToSentenceBoundary from using VisiblePosition

This patch stops the two functions from using VisiblePosition by switch
to the VP-free versions of Start/EndOfSentence(). Hence, this patch
reduces the usage of legacy VisiblePosition.

Bug: 657237
Change-Id: I933a020f9bd6643ba1b2cd5111b8be18b2f49086
Reviewed-on: https://chromium-review.googlesource.com/c/1337816Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608849}

third_party/blink/renderer/core/editing/visible_units.h

@@ -138,6 +138,9 @@ CORE_EXPORT PositionWithAffinity PreviousWordPosition(const Position&);
 CORE_EXPORT PositionWithAffinity NextWordPosition(const Position&);
 
 // sentences
+CORE_EXPORT Position StartOfSentencePosition(const Position&);
+CORE_EXPORT PositionInFlatTree
+StartOfSentencePosition(const PositionInFlatTree&);
 CORE_EXPORT VisiblePosition StartOfSentence(const VisiblePosition&);
 CORE_EXPORT VisiblePositionInFlatTree
 StartOfSentence(const VisiblePositionInFlatTree&);

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

@@ -191,10 +191,8 @@ VisiblePositionInFlatTree EndOfSentence(const VisiblePositionInFlatTree& c) {
 
 EphemeralRange ExpandEndToSentenceBoundary(const EphemeralRange& range) {
   DCHECK(range.IsNotNull());
-  const VisiblePosition& visible_end =
-      CreateVisiblePosition(range.EndPosition());
-  DCHECK(visible_end.IsNotNull());
-  const Position& sentence_end = EndOfSentence(visible_end).DeepEquivalent();
+  const Position& sentence_end =
+      EndOfSentence(range.EndPosition()).GetPosition();
   // TODO(editing-dev): |sentenceEnd < range.endPosition()| is possible,
   // which would trigger a DCHECK in EphemeralRange's constructor if we return
   // it directly. However, this shouldn't happen and needs to be fixed.
@@ -207,11 +205,8 @@ EphemeralRange ExpandEndToSentenceBoundary(const EphemeralRange& range) {
 
 EphemeralRange ExpandRangeToSentenceBoundary(const EphemeralRange& range) {
   DCHECK(range.IsNotNull());
-  const VisiblePosition& visible_start =
-      CreateVisiblePosition(range.StartPosition());
-  DCHECK(visible_start.IsNotNull());
   const Position& sentence_start =
-      StartOfSentence(visible_start).DeepEquivalent();
+      StartOfSentencePosition(range.StartPosition());
   // TODO(editing-dev): |sentenceStart > range.startPosition()| is possible,
   // which would trigger a DCHECK in EphemeralRange's constructor if we return
   // it directly. However, this shouldn't happen and needs to be fixed.