[Merge to M113] preload: add null check in preloading CDPs

This CL adds null check in `DidCancelPrerender` and
`DidUpdatePrefetchStatus` to avoid potential null pointer exception.

(cherry picked from commit 8a6570f)

Bug: 1424609, 1384419
Change-Id: I1aefbee5904ed823b3a5b9ead833db462973f16f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4366038
Commit-Queue: Huanpo Lin <robertlin@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1121498}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4369381
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/branch-heads/5672@{#43}
Cr-Branched-From: 5f2a724-refs/heads/main@{#1121455}

content/browser/devtools/devtools_instrumentation.cc

@@ -434,6 +434,10 @@ void DidCancelPrerender(
     const base::UnguessableToken& initiator_devtools_navigation_token,
     PrerenderFinalStatus status,
     const std::string& disallowed_api_method) {
+  if (!ftn) {
+    return;
+  }
+
   std::string initiating_frame_id =
       ftn->current_frame_host()->devtools_frame_token().ToString();
   DispatchToAgents(ftn, &protocol::PreloadHandler::DidCancelPrerender,
@@ -446,6 +450,10 @@ void DidUpdatePrefetchStatus(
     const base::UnguessableToken& initiator_devtools_navigation_token,
     const GURL& prefetch_url,
     PreloadingTriggeringOutcome status) {
+  if (!ftn) {
+    return;
+  }
+
   std::string initiating_frame_id =
       ftn->current_frame_host()->devtools_frame_token().ToString();
   DispatchToAgents(ftn, &protocol::PreloadHandler::DidUpdatePrefetchStatus,