Have Document::getCSSCanvasElement() return a reference

Source/core/css/CSSCanvasValue.cpp

Index: Source/core/css/CSSCanvasValue.cpp
diff --git a/Source/core/css/CSSCanvasValue.cpp b/Source/core/css/CSSCanvasValue.cpp
index 20c8d1dc1058b9319336785f414848babbc431ea..1514eaceb2c04880d0c2938a951faecdc97e2491 100644
--- a/Source/core/css/CSSCanvasValue.cpp
+++ b/Source/core/css/CSSCanvasValue.cpp
@@ -77,9 +77,7 @@ IntSize CSSCanvasValue::fixedSize(const RenderObject* renderer)
 HTMLCanvasElement* CSSCanvasValue::element(Document* document)
 {
      if (!m_element) {
-        m_element = document->getCSSCanvasElement(m_name);
-        if (!m_element)
-            return 0;
+        m_element = &document->getCSSCanvasElement(m_name);
         m_element->addObserver(&m_canvasObserver);
     }
     return m_element;