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.

libcef/browser/browser_main.cc

@@ -164,10 +164,6 @@ void CefBrowserMainParts::PreMainMessageLoopRun() {
 
   // Triggers initialization of the singleton instance on UI thread.
   PluginFinder::GetInstance()->Init();
-
-#if defined(OS_WIN)
-  PlatformPreMainMessageLoopRun();
-#endif
 }
 
 void CefBrowserMainParts::PostMainMessageLoopRun() {