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/jsdialog_unittest.cc

@@ -91,7 +91,6 @@ class JSDialogTestHandler : public TestHandler {
 
   bool OnJSDialog(CefRefPtr<CefBrowser> browser,
                   const CefString& origin_url,
-                  const CefString& accept_lang,
                   JSDialogType dialog_type,
                   const CefString& message_text,
                   const CefString& default_prompt_text,
@@ -100,7 +99,6 @@ class JSDialogTestHandler : public TestHandler {
     got_onjsdialog_.yes();
 
     EXPECT_STREQ(kStartUrl, origin_url.ToString().c_str());
-    EXPECT_TRUE(accept_lang.empty());
 
     if (type_ == TYPE_ALERT) {
       EXPECT_EQ(JSDIALOGTYPE_ALERT, dialog_type);