Add a FOUC painting test.

Source/web/tests/sim/SimRequest.h

Index: Source/web/tests/sim/SimRequest.h
diff --git a/Source/web/tests/sim/SimRequest.h b/Source/web/tests/sim/SimRequest.h
index 42ba0fe6b398102c86bf15b4c558cf793277d30a..197f2c1bfd2c09c7a91f0b70788a4eb8cb494268 100644
--- a/Source/web/tests/sim/SimRequest.h
+++ b/Source/web/tests/sim/SimRequest.h
@@ -15,25 +15,38 @@ class SimNetwork;
 class WebURLLoader;
 class WebURLLoaderClient;
 
-class SimRequest {
+// Simulates a single request for a resource from the server. Requires a
+// SimNetwork to have been created first. Use the start(), write() and finish()
+// methods to simulate the response from the server. Note that all started
+// requests must be finished.
+class SimRequest final {
 public:
     SimRequest(String url, String mimeType);
+    ~SimRequest();
 
-    void didReceiveResponse(WebURLLoaderClient*, WebURLLoader*, const WebURLResponse&);
-    void didFail(const WebURLError&);
-
+    // Starts the response from the server, this is as if the headers and 200 OK
+    // reply had been received but no response body yet.
     void start();
+
+    // Write a chunk of the response body.
     void write(const String& data);
+
+    // Finish the response, this is as if the server closed the connection.
     void finish();
 
-    bool isReady() const { return m_isReady; }
     const String& url() const { return m_url; }
     const WebURLError& error() const { return m_error; }
     const WebURLResponse& response() const { return m_response; }
 
+private:
+    friend class SimNetwork;
+
     void reset();
 
-private:
+    // Used by SimNetwork.
+    void didReceiveResponse(WebURLLoaderClient*, WebURLLoader*, const WebURLResponse&);
+    void didFail(const WebURLError&);
+
     String m_url;
     WebURLLoader* m_loader;
     WebURLResponse m_response;