headless: Add a small C++ example application

headless/app/headless_shell.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/files/file_proxy.h"
 #include "base/memory/weak_ptr.h"
 #include "headless/app/shell_navigation_request.h"
 #include "headless/public/devtools/domains/emulation.h"
 #include "headless/public/devtools/domains/inspector.h"
 #include "headless/public/devtools/domains/page.h"
 #include "headless/public/devtools/domains/runtime.h"
 #include "headless/public/headless_browser.h"
 #include "headless/public/headless_devtools_client.h"
 #include "headless/public/headless_web_contents.h"
 #include "headless/public/util/deterministic_dispatcher.h"
 #include "net/base/file_stream.h"
 
 namespace headless {
 
 // An application which implements a simple headless browser.
 class HeadlessShell : public HeadlessWebContents::Observer,
-                      emulation::ExperimentalObserver,
-                      inspector::ExperimentalObserver,
-                      page::ExperimentalObserver {
+                      public emulation::ExperimentalObserver,
+                      public inspector::ExperimentalObserver,
+                      public page::ExperimentalObserver {
  public:
   HeadlessShell();
   ~HeadlessShell() override;
 
   // HeadlessWebContents::Observer implementation:
   void DevToolsTargetReady() override;
   void OnTargetCrashed(const inspector::TargetCrashedParams& params) override;
 
   // emulation::Observer implementation:
   void OnVirtualTimeBudgetExpired(
@@ skipping 54 matching lines @@
   bool processed_page_ready_;
   std::unique_ptr<base::FileProxy> screenshot_file_proxy_;
   HeadlessBrowserContext* browser_context_;
   std::unique_ptr<DeterministicDispatcher> deterministic_dispatcher_;
   base::WeakPtrFactory<HeadlessShell> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessShell);
 };
 
 }  // namespace headless