Added 'contextReady' message for HostPairingScreen.

Sometimes the screen starts to send updates to JS part to early, when screen
is not registered yet. As a result several messages with context diffs could
be ignored, and JS context became inconsistent with C++ context. I added
'contextReady' message, that is send from JS when context is ready to recieve
updates. Before that the screen handler caches changes in the local context.

BUG=375191

Review URL: https://codereview.chromium.org/581593003

Cr-Commit-Position: refs/heads/master@{#295944}

chrome/browser/chromeos/login/screens/screen_context.h

@@ -84,6 +84,9 @@ class ScreenContext : public base::NonThreadSafe {
   void ApplyChanges(const base::DictionaryValue& diff,
                     std::vector<std::string>* keys);
 
+  // Returns underlying dictionary containing all the stored data.
+  const base::DictionaryValue& storage() const { return storage_; }
+
  private:
   bool Set(const KeyType& key, base::Value* value);
 

chrome/browser/resources/chromeos/login/oobe_screen_host_pairing.js

@@ -25,6 +25,9 @@ login.createScreen('HostPairingScreen', 'host-pairing', function() {
   /** @const */ var PAGE_ENROLLMENT_ERROR = 'enrollment-error';
   /** @const */ var PAGE_PAIRING_DONE = 'pairing-done';
 
+  /** @const */ var CALLBACK_CONTEXT_READY = 'contextReady';
+
+
   /** @const */ var PAGE_NAMES = [
       PAGE_WELCOME,
       PAGE_CODE_CONFIRMATION,
@@ -51,6 +54,7 @@ login.createScreen('HostPairingScreen', 'host-pairing', function() {
       }, this);
 
       this.addContextObserver(CONTEXT_KEY_PAGE, this.pageChanged_);
+      this.send(CALLBACK_CONTEXT_READY);
     },
 
     pageChanged_: function(newPage, oldPage) {

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);
 }
 

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

@@ -7,6 +7,7 @@
 
 #include "base/macros.h"
 #include "chrome/browser/chromeos/login/screens/host_pairing_screen_actor.h"
+#include "chrome/browser/chromeos/login/screens/screen_context.h"
 #include "chrome/browser/ui/webui/chromeos/login/base_screen_handler.h"
 
 namespace chromeos {
@@ -18,6 +19,8 @@ class HostPairingScreenHandler : public HostPairingScreenActor,
   virtual ~HostPairingScreenHandler();
 
  private:
+  void HandleContextReady();
+
   // Overridden from BaseScreenHandler:
   virtual void Initialize() OVERRIDE;
   virtual void DeclareLocalizedValues(LocalizedValuesBuilder* builder) OVERRIDE;
@@ -33,6 +36,10 @@ class HostPairingScreenHandler : public HostPairingScreenActor,
 
   HostPairingScreenActor::Delegate* delegate_;
   bool show_on_init_;
+  bool js_context_ready_;
+
+  // Caches context changes while JS part is not ready to receive messages.
+  ScreenContext context_cache_;
 
   DISALLOW_COPY_AND_ASSIGN(HostPairingScreenHandler);
 };