Update signin intercept to Guest mode edge cases.

Two cases are updated for signin intercept to Guest mode:
 1- When Guest mode is disabled by policy, this will not be offered.
 2- If user opens a Guest profile whie signin intercept is showing,
    and chooses to go to Guest mode, this will be done.

Bug: 1157764
Change-Id: I4116b2c32125a76d893911eebe1c2c31b2284231
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2620559Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841956}

chrome/browser/signin/dice_signed_in_profile_creator.cc

@@ -141,12 +141,16 @@ DiceSignedInProfileCreator::DiceSignedInProfileCreator(
       callback_(std::move(callback)) {
   if (use_guest_profile) {
     DCHECK(Profile::IsEphemeralGuestProfileEnabled());
-    DCHECK(!ProfileManager::GuestProfileExists());
-    g_browser_process->profile_manager()->CreateProfileAsync(
-        ProfileManager::GetGuestProfilePath(),
-        base::BindRepeating(&DiceSignedInProfileCreator::OnNewProfileCreated,
-                            weak_pointer_factory_.GetWeakPtr()),
-        base::string16(), std::string());
+    // Make sure the callback is not called synchronously.
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::BindOnce(&ProfileManager::CreateProfileAsync,
+                       base::Unretained(g_browser_process->profile_manager()),
+                       ProfileManager::GetGuestProfilePath(),
+                       base::BindRepeating(
+                           &DiceSignedInProfileCreator::OnNewProfileCreated,
+                           weak_pointer_factory_.GetWeakPtr()),
+                       base::string16(), std::string()));
   } else {
     ProfileAttributesStorage& storage =
         g_browser_process->profile_manager()->GetProfileAttributesStorage();

chrome/browser/signin/dice_web_signin_interceptor.cc

@@ -90,7 +90,9 @@ bool HasNoBrowser(content::WebContents* web_contents) {
 
 bool GuestOptionAvailable() {
   return Profile::IsEphemeralGuestProfileEnabled() &&
-         !ProfileManager::GuestProfileExists();
+         !ProfileManager::GuestProfileExists() &&
+         g_browser_process->local_state()->GetBoolean(
+             prefs::kBrowserGuestModeEnabled);
 }
 
 }  // namespace