Improve VisibleUnitsTest.localCaretRectOfPosition

This patch changes |VisibleUnitsTest.localCaretRectOfPosition| to check
results of |localCaretRectOfPosition()| aren't empty for improving detection
of regression.

This is a follow-up patch for http://crrev.com/1317503002, which introduces
composed tree version of | localCaretRectOfPosition()|.

BUG=513568
TEST=webkit_unit_tests --gtest_filter=VisibleUnitsTest.localCaretRectOfPosition

Review URL: https://codereview.chromium.org/1319623004

git-svn-id: svn://svn.chromium.org/blink/trunk@201186 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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

@@ -63,11 +63,13 @@ TEST_F(VisibleUnitsTest, localCaretRectOfPosition)
     RefPtrWillBeRawPtr<Element> one = document().getElementById("one");
 
     LayoutObject* layoutObjectFromDOMTree;
-    LayoutRect layoutRectFromDOMTree = localCaretRectOfPosition(Position(one, 0), layoutObjectFromDOMTree);
+    LayoutRect layoutRectFromDOMTree = localCaretRectOfPosition(Position(one->firstChild(), 0), layoutObjectFromDOMTree);
 
     LayoutObject* layoutObjectFromComposedTree;
-    LayoutRect layoutRectFromComposedTree = localCaretRectOfPosition(PositionInComposedTree(one, 0), layoutObjectFromComposedTree);
+    LayoutRect layoutRectFromComposedTree = localCaretRectOfPosition(PositionInComposedTree(one->firstChild(), 0), layoutObjectFromComposedTree);
 
+    EXPECT_TRUE(layoutObjectFromDOMTree);
+    EXPECT_FALSE(layoutRectFromDOMTree.isEmpty());
     EXPECT_EQ(layoutObjectFromDOMTree, layoutObjectFromComposedTree);
     EXPECT_EQ(layoutRectFromDOMTree, layoutRectFromComposedTree);
 }