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_platform_delegate.cc

@@ -108,21 +108,12 @@ void CefBrowserPlatformDelegate::SizeTo(int width, int height) {
 }
 #endif
 
-#if defined(OS_MACOSX)
-void CefBrowserPlatformDelegate::SetWindowVisibility(bool visible) {
-  content::RenderWidgetHostView* view =
-      browser_->web_contents()->GetRenderWidgetHostView();
-  if (view)
-    view->SetWindowVisibility(visible);
-}
-#endif
-
-scoped_ptr<CefFileDialogRunner>
+std::unique_ptr<CefFileDialogRunner>
     CefBrowserPlatformDelegate::CreateFileDialogRunner() {
   return nullptr;
 }
 
-scoped_ptr<CefJavaScriptDialogRunner>
+std::unique_ptr<CefJavaScriptDialogRunner>
     CefBrowserPlatformDelegate::CreateJavaScriptDialogRunner() {
   return nullptr;
 }