[STTS] add null check to on delete

(cherry picked from commit 7fa1a05)

(cherry picked from commit 507e4f6)

(cherry picked from commit c0e9da7)

Bug: 1326139
Change-Id: I258d5600d3a0655f307435a1e95332db95835c01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3653120
Reviewed-by: Travis Skare <skare@chromium.org>
Commit-Queue: Jeffrey Cohen <jeffreycohen@chromium.org>
Cr-Original-Original-Original-Commit-Position: refs/heads/main@{#1004523}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3652385
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Krishna Govind <govind@chromium.org>
Cr-Original-Original-Commit-Position: refs/branch-heads/5068@{#3}
Cr-Original-Original-Branched-From: aaa5d2b-refs/heads/main@{#1004201}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3652386
Cr-Original-Commit-Position: refs/branch-heads/5069@{#3}
Cr-Original-Branched-From: 3aaabf4-refs/heads/main@{#1004520}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3654134
Commit-Queue: Krishna Govind <govind@chromium.org>
Reviewed-by: Krishna Govind <govind@chromium.org>
Reviewed-by: Jeffrey Cohen <jeffreycohen@chromium.org>
Cr-Commit-Position: refs/branch-heads/5060@{#81}
Cr-Branched-From: b83393d-refs/heads/main@{#1002911}

components/send_tab_to_self/send_tab_to_self_bridge.cc

@@ -720,7 +720,8 @@ void SendTabToSelfBridge::DeleteEntries(const std::vector<GURL>& urls) {
   for (const GURL& url : urls) {
     auto entry = entries_.begin();
     while (entry != entries_.end()) {
-      bool to_delete = (url == entry->second->GetURL());
+      bool to_delete =
+          (entry->second == nullptr || url == entry->second->GetURL());
 
       std::string guid = entry->first;
       entry++;