Make DummyPageHolder to have all empty clients

Source/core/testing/DummyPageHolder.cpp

Index: Source/core/testing/DummyPageHolder.cpp
diff --git a/Source/core/testing/DummyPageHolder.cpp b/Source/core/testing/DummyPageHolder.cpp
index 1014a150bf11689172a851bce476bbbaf788e0e9..7ca038db0840386a0fc765d1d13b3455f54408f0 100644
--- a/Source/core/testing/DummyPageHolder.cpp
+++ b/Source/core/testing/DummyPageHolder.cpp
@@ -46,13 +46,7 @@ PassOwnPtr<DummyPageHolder> DummyPageHolder::create(const IntSize& initialViewSi
 
 DummyPageHolder::DummyPageHolder(const IntSize& initialViewSize)
 {
-    m_pageClients.chromeClient = &m_chromeClient;
-    m_pageClients.contextMenuClient = &m_contextMenuClient;
-    m_pageClients.editorClient = &m_editorClient;
-    m_pageClients.dragClient = &m_dragClient;
-    m_pageClients.inspectorClient = &m_inspectorClient;
-    m_pageClients.backForwardClient = &m_backForwardClient;
-
+    fillWithEmptyClients(m_pageClients);
     m_page = adoptPtrWillBeNoop(new Page(m_pageClients));
     Settings& settings = m_page->settings();
     // FIXME: http://crbug.com/363843. This needs to find a better way to