Add pixel readback to page popup

Source/web/WebPagePopupImpl.h

Index: Source/web/WebPagePopupImpl.h
diff --git a/Source/web/WebPagePopupImpl.h b/Source/web/WebPagePopupImpl.h
index 99f259ef5265f084d9ac233642da995938ac1097..fccef2cd8734524d5c168410e7adbbbce6cb27c8 100644
--- a/Source/web/WebPagePopupImpl.h
+++ b/Source/web/WebPagePopupImpl.h
@@ -47,6 +47,7 @@ class PlatformKeyboardEvent;
 class WebLayerTreeView;
 class WebLayer;
 class WebViewImpl;
+class LocalDOMWindow;
 
 class WebPagePopupImpl FINAL
     : public WebPagePopup
@@ -63,6 +64,9 @@ public:
     void closePopup();
     WebWidgetClient* widgetClient() const { return m_widgetClient; }
     bool hasSamePopupClient(WebPagePopupImpl* other) { return other && m_popupClient == other->m_popupClient; }
+    virtual void compositeAndReadbackAsync(WebCompositeAndReadbackAsyncCallback*) OVERRIDE;
+    LocalDOMWindow* window();
+    virtual WebPoint relativePosition() OVERRIDE;
 
 private:
     // WebWidget functions