[SendTabToSelf] Potentially fixed sigsev in ShouldOfferFeature.

The function assumed that all calls would return non-null pointers.
Fixed that to explictly check for nullptr.

Bug: 950640
Change-Id: I7b1ff107b3dd6b94b439f486779cfefe2ae1688e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1577977Reviewed-by: sebsg <sebsg@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Tanya Gupta <tgupta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653360}

chrome/browser/send_tab_to_self/send_tab_to_self_util.cc

@@ -34,15 +34,19 @@ bool IsSendingEnabled() {
 }
 
 bool IsUserSyncTypeActive(Profile* profile) {
-  return SendTabToSelfSyncServiceFactory::GetForProfile(profile)
-      ->GetSendTabToSelfModel()
-      ->IsReady();
+  SendTabToSelfSyncService* service =
+      SendTabToSelfSyncServiceFactory::GetForProfile(profile);
+  // The service will be null if the user is in incognito mode so better to
+  // check for that.
+  return service && service->GetSendTabToSelfModel() &&
+         service->GetSendTabToSelfModel()->IsReady();
 }
 
 bool IsSyncingOnMultipleDevices(Profile* profile) {
   syncer::DeviceInfoSyncService* device_sync_service =
       DeviceInfoSyncServiceFactory::GetForProfile(profile);
-  return device_sync_service &&
+
+  return device_sync_service && device_sync_service->GetDeviceInfoTracker() &&
          device_sync_service->GetDeviceInfoTracker()->CountActiveDevices() > 1;
 }
 
@@ -55,8 +59,9 @@ bool IsContentRequirementsMet(const GURL& url, Profile* profile) {
 }
 
 bool ShouldOfferFeature(content::WebContents* web_contents) {
-  if (!web_contents)
+  if (!web_contents) {
     return false;
+  }
   Profile* profile =
       Profile::FromBrowserContext(web_contents->GetBrowserContext());