Make DisplayItemClient an interface

third_party/WebKit/Source/web/WebFontImpl.h

Index: third_party/WebKit/Source/web/WebFontImpl.h
diff --git a/third_party/WebKit/Source/web/WebFontImpl.h b/third_party/WebKit/Source/web/WebFontImpl.h
index b6c2378f65f09dd488c189496a72c2631afbb7fc..2929dcf4bd2e0e6a96f29528c6d3e2e5eaaf672d 100644
--- a/third_party/WebKit/Source/web/WebFontImpl.h
+++ b/third_party/WebKit/Source/web/WebFontImpl.h
@@ -39,7 +39,7 @@ namespace blink {
 
 class FontDescription;
 
-class WebFontImpl final : public WebFont {
+class WebFontImpl final : public WebFont, public DisplayItemClient {
 public:
     explicit WebFontImpl(const FontDescription&);
 
@@ -59,8 +59,7 @@ public:
     WebFloatRect selectionRectForText(const WebTextRun&, const WebFloatPoint& leftBaseline,
         int height, int from = 0, int to = -1) const override;
 
-    DisplayItemClient displayItemClient() const { return toDisplayItemClient(this); }
-    String debugName() const { return "WebFontImpl"; }
+    String debugName() const final { return "WebFontImpl"; }
 
 private:
     Font m_font;