Fix missing HEADLESS_EXPORT defines

headless/public/headless_web_contents.h

 // Copyright 2015 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.
 
 #ifndef HEADLESS_PUBLIC_HEADLESS_WEB_CONTENTS_H_
 #define HEADLESS_PUBLIC_HEADLESS_WEB_CONTENTS_H_
 
 #include <list>
 #include <string>
 #include <utility>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/process/kill.h"
 #include "headless/public/headless_export.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "ui/gfx/geometry/size.h"
 #include "url/gurl.h"
 
 namespace headless {
 class HeadlessBrowserContextImpl;
 class HeadlessBrowserImpl;
 class HeadlessDevToolsTarget;
 
 // Class representing contents of a browser tab. Should be accessed from browser
 // main thread.
 class HEADLESS_EXPORT HeadlessWebContents {
  public:
-  class Builder;
+  class HEADLESS_EXPORT Builder;
 
   virtual ~HeadlessWebContents() {}
 
-  class Observer {
+  class HEADLESS_EXPORT Observer {
    public:
     // All the following notifications will be called on browser main thread.
 
     // Indicates that this HeadlessWebContents instance is now ready to be
     // inspected using a HeadlessDevToolsClient.
     //
     // TODO(altimin): Support this event for pages that aren't created by us.
     virtual void DevToolsTargetReady() {}
 
     // This method is invoked when the process of the observed RenderProcessHost
@@ skipping 102 matching lines @@
   GURL initial_url_ = GURL("about:blank");
   gfx::Size window_size_;
   std::list<MojoService> mojo_services_;
 
   DISALLOW_COPY_AND_ASSIGN(Builder);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_HEADLESS_WEB_CONTENTS_H_