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}

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

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