convert //headless to std::unique_ptr

headless/app/headless_shell.cc

Index: headless/app/headless_shell.cc
diff --git a/headless/app/headless_shell.cc b/headless/app/headless_shell.cc
index b04d7760e75def88f58c90d1ca15087b3d1c3c66..e2d6348cf4285589d62c1a61f0ce7f2c113cf190 100644
--- a/headless/app/headless_shell.cc
+++ b/headless/app/headless_shell.cc
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <memory>
+
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/command_line.h"
@@ -73,7 +75,7 @@ class HeadlessShell : public HeadlessWebContents::Observer {
 
  private:
   HeadlessBrowser* browser_;  // Not owned.
-  scoped_ptr<HeadlessWebContents> web_contents_;
+  std::unique_ptr<HeadlessWebContents> web_contents_;
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessShell);
 };