Add support for media device discovery and messaging (fixes issue #2900)

Chromium supports communication with media devices on the local network via
the Cast and DIAL protocols. This takes two primary forms:

1. Messaging, where strings representing state information are passed between
   the client and a dedicated receiver app on the media device. The receiver
   app communicates directly with an app-specific backend service to retrieve
   and possibly control media playback.
2. Tab/desktop mirroring, where the media contents are streamed directly from
   the browser to a generic streaming app on the media device and playback is
   controlled by the browser.

This change adds support for device discovery and messaging (but not
mirroring) with functionality exposed via the new CefMediaRouter interface.

To test: Navigate to http://tests/media_router in cefclient and follow the
on-screen instructions.

libcef_dll/cpptoc/request_context_cpptoc.cc

@@ -9,13 +9,14 @@
 // implementations. See the translator.README.txt file in the tools directory
 // for more information.
 //
-// $hash=4af6d074b7de62b759a9555a0b0246e57c290328$
+// $hash=5168000f75f7911dce0bffcf47341e4ee1c2a275$
 //
 
 #include "libcef_dll/cpptoc/request_context_cpptoc.h"
 #include "libcef_dll/cpptoc/cookie_manager_cpptoc.h"
 #include "libcef_dll/cpptoc/dictionary_value_cpptoc.h"
 #include "libcef_dll/cpptoc/extension_cpptoc.h"
+#include "libcef_dll/cpptoc/media_router_cpptoc.h"
 #include "libcef_dll/cpptoc/value_cpptoc.h"
 #include "libcef_dll/ctocpp/completion_callback_ctocpp.h"
 #include "libcef_dll/ctocpp/extension_handler_ctocpp.h"
@@ -540,6 +541,22 @@ request_context_get_extension(struct _cef_request_context_t* self,
   return CefExtensionCppToC::Wrap(_retval);
 }
 
+cef_media_router_t* CEF_CALLBACK
+request_context_get_media_router(struct _cef_request_context_t* self) {
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return NULL;
+
+  // Execute
+  CefRefPtr<CefMediaRouter> _retval =
+      CefRequestContextCppToC::Get(self)->GetMediaRouter();
+
+  // Return type: refptr_same
+  return CefMediaRouterCppToC::Wrap(_retval);
+}
+
 }  // namespace
 
 // CONSTRUCTOR - Do not edit by hand.
@@ -573,6 +590,7 @@ CefRequestContextCppToC::CefRequestContextCppToC() {
   GetStruct()->has_extension = request_context_has_extension;
   GetStruct()->get_extensions = request_context_get_extensions;
   GetStruct()->get_extension = request_context_get_extension;
+  GetStruct()->get_media_router = request_context_get_media_router;
 }
 
 // DESTRUCTOR - Do not edit by hand.