Added 'contextReady' message for HostPairingScreen.

chrome/browser/ui/webui/chromeos/login/host_pairing_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/host_pairing_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/host_pairing_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/host_pairing_screen_handler.cc
index dda343c5a7e94d586470b7b8de60419bc7e1efa0..6a1ffcb90762ed965a14f0a37dbdc3ebff146b71 100644
--- a/chrome/browser/ui/webui/chromeos/login/host_pairing_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/host_pairing_screen_handler.cc
@@ -14,10 +14,18 @@ const char kJsScreenPath[] = "login.HostPairingScreen";
 
 const char kMethodContextChanged[] = "contextChanged";
 
+// Sent from JS when screen is ready to receive context updates.
+// TODO(dzhioev): Move 'contextReady' logic to the base screen handler when
+// all screens migrate to context-based communications.
+const char kCallbackContextReady[] = "contextReady";
+
 }  // namespace
 
 HostPairingScreenHandler::HostPairingScreenHandler()
-    : BaseScreenHandler(kJsScreenPath), delegate_(NULL), show_on_init_(false) {
+    : BaseScreenHandler(kJsScreenPath),
+      delegate_(NULL),
+      show_on_init_(false),
+      js_context_ready_(false) {
 }
 
 HostPairingScreenHandler::~HostPairingScreenHandler() {
@@ -25,6 +33,11 @@ HostPairingScreenHandler::~HostPairingScreenHandler() {
     delegate_->OnActorDestroyed(this);
 }
 
+void HostPairingScreenHandler::HandleContextReady() {
+  js_context_ready_ = true;
+  OnContextChanged(context_cache_.storage());
+}
+
 void HostPairingScreenHandler::Initialize() {
   if (!page_is_ready() || !delegate_)
     return;
@@ -40,6 +53,8 @@ void HostPairingScreenHandler::DeclareLocalizedValues(
 }
 
 void HostPairingScreenHandler::RegisterMessages() {
+  AddPrefixedCallback(kCallbackContextReady,
+                      &HostPairingScreenHandler::HandleContextReady);
 }
 
 void HostPairingScreenHandler::Show() {
@@ -61,6 +76,10 @@ void HostPairingScreenHandler::SetDelegate(Delegate* delegate) {
 
 void HostPairingScreenHandler::OnContextChanged(
     const base::DictionaryValue& diff) {
+  if (!js_context_ready_) {
+    context_cache_.ApplyChanges(diff, NULL);
+    return;
+  }
   CallJS(kMethodContextChanged, diff);
 }