Make VisiblePosition constructor to canonicalize a position in composed tree

Source/core/editing/VisiblePositionTest.cpp

Index: Source/core/editing/VisiblePositionTest.cpp
diff --git a/Source/core/editing/VisiblePositionTest.cpp b/Source/core/editing/VisiblePositionTest.cpp
index ad5145d184769f629f524caff4eec6fdcf6af177..3699a16d8631e6ffbc0c27b04e0c33ce656b99b7 100644
--- a/Source/core/editing/VisiblePositionTest.cpp
+++ b/Source/core/editing/VisiblePositionTest.cpp
@@ -26,10 +26,14 @@ TEST_F(VisiblePositionTest, ShadowDistributedNodes)
     RefPtrWillBeRawPtr<Element> five = shadowRoot->querySelector("#s5", ASSERT_NO_EXCEPTION);
 
     EXPECT_EQ(positionInDOMTree(*one->firstChild(), 0), canonicalPositionOf(positionInDOMTree(*one, 0)));
+    EXPECT_EQ(positionInDOMTree(*one->firstChild(), 0), VisiblePosition(positionInDOMTree(*one, 0)).deepEquivalent());
     EXPECT_EQ(positionInDOMTree(*one->firstChild(), 2), canonicalPositionOf(positionInDOMTree(*two, 0)));
+    EXPECT_EQ(positionInDOMTree(*one->firstChild(), 2), VisiblePosition(positionInDOMTree(*two, 0)).deepEquivalent());
 
     EXPECT_EQ(positionInComposedTree(*five->firstChild(), 2), canonicalPositionOf(positionInComposedTree(*one, 0)));
+    EXPECT_EQ(positionInDOMTree(*five->firstChild(), 2), VisiblePosition(positionInComposedTree(*one, 0)).deepEquivalent());
     EXPECT_EQ(positionInComposedTree(*four->firstChild(), 2), canonicalPositionOf(positionInComposedTree(*two, 0)));
+    EXPECT_EQ(positionInDOMTree(*four->firstChild(), 2), VisiblePosition(positionInComposedTree(*two, 0)).deepEquivalent());
 }
 
 } // namespace blink