[NotLanded] Implement the fetching algorithm of the Web Manifest.

public/web/WebFrame.h

Index: public/web/WebFrame.h
diff --git a/public/web/WebFrame.h b/public/web/WebFrame.h
index d630f801834c1614177372f90fccbcb1fbaf5bcd..9004405faace69a756a6147cbca7a197f8fe0990 100644
--- a/public/web/WebFrame.h
+++ b/public/web/WebFrame.h
@@ -70,6 +70,7 @@ class WebFrameClient;
 class WebInputElement;
 class WebLayer;
 class WebLocalFrame;
+class WebManifestRequest;
 class WebPerformance;
 class WebPermissionClient;
 class WebRange;
@@ -675,6 +676,12 @@ public:
     // text form. This is used only by layout tests.
     virtual WebString layerTreeAsText(bool showDebugInfo = false) const = 0;
 
+    // Manifest ------------------------------------------------------------
+
+    // Starts fetching and parsing the manifest. The passed WebManifestRequest
+    // will get notified when the request ends, whether it failed or succeeded.
+    virtual void requestManifest(WebManifestRequest&) const = 0;
+
 protected:
     explicit WebFrame();
     virtual ~WebFrame();