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/osr/render_widget_host_view_osr_win.cc

@@ -143,19 +143,6 @@ bool IsSystemCursorID(LPCWSTR cursor_id) {
 
 }  // namespace
 
-void CefRenderWidgetHostViewOSR::SetParentNativeViewAccessible(
-    gfx::NativeViewAccessible accessible_parent) {
-}
-
-gfx::NativeViewId
-    CefRenderWidgetHostViewOSR::GetParentForWindowlessPlugin() const {
-  if (browser_impl_.get()) {
-    return reinterpret_cast<gfx::NativeViewId>(
-        browser_impl_->GetWindowHandle());
-  }
-  return NULL;
-}
-
 void CefRenderWidgetHostViewOSR::PlatformCreateCompositorWidget() {
   DCHECK(!window_);
   window_.reset(new CefCompositorHostWin());