Use EditingTestBase for PositionTest

Source/core/editing/EditingTestBase.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/editing/EditingTestBase.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Range.h"
 #include "core/dom/Text.h"
@@ skipping 27 matching lines @@
     return shadowRoot.release();
 }
 
 void EditingTestBase::setBodyContent(const char* bodyContent)
 {
     document().body()->setInnerHTML(String::fromUTF8(bodyContent), ASSERT_NO_EXCEPTION);
 }
 
 PassRefPtrWillBeRawPtr<ShadowRoot> EditingTestBase::setShadowContent(const char* shadowContent)
 {
-    return createShadowRootForElementWithIDAndSetInnerHTML(document(), "host", shadowContent);
+    RefPtrWillBeRawPtr<ShadowRoot> shadowRoot = createShadowRootForElementWithIDAndSetInnerHTML(document(), "host", shadowContent);
+    document().recalcDistribution();
+    return shadowRoot.release();
 }
 
 Position EditingTestBase::positionInDOMTree(Node& anchor, int offset)
 {
     return Position(&anchor, offset, Position::PositionIsOffsetInAnchor);
 }
 
 PositionInComposedTree EditingTestBase::positionInComposedTree(Node& anchor, int offset)
 {
     return PositionInComposedTree(&anchor, offset, PositionInComposedTree::PositionIsOffsetInAnchor);
 }
 
 } // namespace blink