headless: Require the user to pass in an initial URL

headless/public/headless_web_contents.h

Index: headless/public/headless_web_contents.h
diff --git a/headless/public/headless_web_contents.h b/headless/public/headless_web_contents.h
index e3cfbfb3ad86b98c5438497d0658746f8062f3a1..04ac953001d61b94e9d9bab75de4ea1a931ef0fa 100644
--- a/headless/public/headless_web_contents.h
+++ b/headless/public/headless_web_contents.h
@@ -22,9 +22,13 @@ class HEADLESS_EXPORT HeadlessWebContents {
   // TODO(skyostil): Replace this with an equivalent client API.
   class Observer {
    public:
-    // Will be called on browser thread.
-    virtual void DocumentOnLoadCompletedInMainFrame() = 0;
-    virtual void DidFinishNavigation(bool success) = 0;
+    // All the following notifications will be called on browser main thread.
+    virtual void DocumentOnLoadCompletedInMainFrame(){};
+    virtual void DidFinishNavigation(bool success){};
+
+    // After this event, this HeadlessWebContents instance is ready to be
+    // controlled using a DevTools client.
+    virtual void WebContentsReady(){};
 
    protected:
     Observer() {}
@@ -34,9 +38,6 @@ class HEADLESS_EXPORT HeadlessWebContents {
     DISALLOW_COPY_AND_ASSIGN(Observer);
   };
 
-  // TODO(skyostil): Replace this with an equivalent client API.
-  virtual bool OpenURL(const GURL& url) = 0;
-
   // Add or remove an observer to receive events from this WebContents.
   // |observer| must outlive this class or be removed prior to being destroyed.
   virtual void AddObserver(Observer* observer) = 0;