Make LayoutSelectionTest.FirstLetterClearSeletion simpler

This patch makes |LayoutSelectionTest.FirstLetterClearSeletion| simpler for
improving code health.

Change-Id: I316057bc63acb597cc2a2575a9416ae8b0eaf927
Reviewed-on: https://chromium-review.googlesource.com/702195
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506978}

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

@@ -305,15 +305,8 @@ TEST_F(LayoutSelectionTest, FirstLetter) {
 }
 
 TEST_F(LayoutSelectionTest, FirstLetterClearSeletion) {
-  SetBodyContent(
-      "<style>div::first-letter { color: red; }</style>"
-      "foo<div>bar</div>baz");
-  Node* foo = GetDocument().body()->firstChild()->nextSibling();
-  // <div>fo^o</div><div>bar</div>b|az
-  Selection().SetSelection(
-      SelectionInDOMTree::Builder()
-          .SetBaseAndExtent({foo, 2}, {foo->nextSibling()->nextSibling(), 1})
-          .Build());
+  InsertStyleElement("div::first-letter { color: red; }");
+  Selection().SetSelection(SetSelectionTextToBody("fo^o<div>bar</div>b|az"));
   Selection().CommitAppearanceIfNeeded();
   TEST_NEXT(IsLayoutBlock, kStartAndEnd, ShouldInvalidate);
   TEST_NEXT(IsLayoutBlock, kStart, ShouldInvalidate);