Print Preview: Check that mirror or dice is enabled to add observer

The identity manager creates a browser crash if AddObserver is called
in incognito. Check that either mirror or dice is enabled before
getting the manager and adding the observer.

Bug: 968084
Change-Id: I4017eeada1732172cd7a731b64e9d8d1f69cf9a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1635634Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664397}

chrome/browser/ui/webui/print_preview/print_preview_handler.cc

@@ -1327,6 +1327,11 @@ void PrintPreviewHandler::RegisterForGaiaCookieChanges() {
     return;
 
   Profile* profile = Profile::FromWebUI(web_ui());
+  if (!AccountConsistencyModeManager::IsMirrorEnabledForProfile(profile) &&
+      !AccountConsistencyModeManager::IsDiceEnabledForProfile(profile)) {
+    return;
+  }
+
   identity_manager_ = IdentityManagerFactory::GetForProfile(profile);
   identity_manager_->AddObserver(this);
 }