Extensions: WAR: GUID: Replace CHECK() with if() to avoid crashing

Method with recent CHECK()'s added that have now been changed to if():
* IsResourceWebAccessibleRedirect()

Context:
* crrev.com/c/5691042
* crrev.com/c/5692819
* crrev.com/c/5636785/comment/c54e7248_e72c9dff/
* crrev.com/c/5636785/comment/51f768f3_3474ec90/

Fixed: chromium:352445642
Change-Id: I243d83e6d65d8d04604ef20aa12fafc3feef4705
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5693030
Auto-Submit: Solomon Kinard <solomonkinard@chromium.org>
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1326035}
diff --git a/extensions/common/manifest_handlers/web_accessible_resources_info.cc b/extensions/common/manifest_handlers/web_accessible_resources_info.cc
index b7dbaa868..1eb17d5 100644
--- a/extensions/common/manifest_handlers/web_accessible_resources_info.cc
+++ b/extensions/common/manifest_handlers/web_accessible_resources_info.cc
@@ -252,7 +252,9 @@
     const GURL& target_url) {
   CHECK(extension);
   CHECK(target_url.SchemeIs(kExtensionScheme));
-  CHECK(upstream_url.is_empty() || upstream_url.SchemeIs(kExtensionScheme));
+  if (!upstream_url.is_empty() && !upstream_url.SchemeIs(kExtensionScheme)) {
+    return false;
+  }
 
   return IsResourceWebAccessibleImpl(*extension, initiator_origin, upstream_url,
                                      target_url);