Update to Chromium revision 6e53600d (#386251)

- Remove |accept_lang| parameter from CefJSDialogHandler::OnJSDialog
  and CefFormatUrlForSecurityDisplay (see https://crbug.com/336973#c36).
- Remove remaining NPAPI-related code including functions from
  cef_web_plugin.h (see https://crbug.com/493212#c55).
- Mac: 10.7+ deployment target is now required for client applications.
- Mac: Remove CefBrowserHost::SetWindowVisibility (issue #1375). No
  replacement is required for windowed rendering. Use WasHidden for
  off-screen rendering.
- Windows: Visual Studio 2015 Update 2 is now required when building
  CEF/Chromium.

tests/unittests/run_all_unittests.cc

@@ -171,7 +171,7 @@ int main(int argc, char* argv[]) {
     retval = test_suite.Run();
   } else {
     // Create the test thread.
-    scoped_ptr<CefTestThread> thread;
+    std::unique_ptr<CefTestThread> thread;
     thread.reset(new CefTestThread(&test_suite));
     if (!thread->Start())
       return 1;