Revert "Change Range::expand() to VisiblePosition-free functions for word and sentence"

This reverts commit 775938b6.

Reason for revert: need to revert this to revert r608849

Original change's description:
> Change Range::expand() to VisiblePosition-free functions for word and sentence
> 
> This patch changes Range::expand() to call VP-free version of word and
> sentence start/end functions, by hoisting the creation of VP from
> the functions into itself. In this way we reduce the usage of functions
> relying on VP.
> 
> Bug: 657237
> Change-Id: I56ea3cb88972144887eba7701cfdc3628bdbf67b
> Reviewed-on: https://chromium-review.googlesource.com/c/1338719
> Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
> Reviewed-by: Kent Tamura <tkent@chromium.org>
> Reviewed-by: Yoichi Osato <yoichio@chromium.org>
> Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#608855}

TBR=yosin@chromium.org,tkent@chromium.org,yoichio@chromium.org,xiaochengh@chromium.org

Bug: 657237, 906174
Change-Id: I46b8df3cfd8ed7f7636f9ef1dabfa350168cb820
Reviewed-on: https://chromium-review.googlesource.com/c/1340906Reviewed-by: Ella Ge <eirage@chromium.org>
Commit-Queue: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608957}

third_party/blink/renderer/core/dom/range.cc

@@ -1618,12 +1618,11 @@ void Range::expand(const String& unit, ExceptionState& exception_state) {
   VisiblePosition start = CreateVisiblePosition(StartPosition());
   VisiblePosition end = CreateVisiblePosition(EndPosition());
   if (unit == "word") {
-    start = CreateVisiblePosition(StartOfWordPosition(start.DeepEquivalent()));
-    end = CreateVisiblePosition(EndOfWordPosition(end.DeepEquivalent()));
+    start = StartOfWord(start);
+    end = EndOfWord(end);
   } else if (unit == "sentence") {
-    start =
-        CreateVisiblePosition(StartOfSentencePosition(start.DeepEquivalent()));
-    end = CreateVisiblePosition(EndOfSentence(end.DeepEquivalent()));
+    start = StartOfSentence(start);
+    end = EndOfSentence(end);
   } else if (unit == "block") {
     start = StartOfParagraph(start);
     end = EndOfParagraph(end);